Según la sempiterna Wikipedia un API es …
«API (del inglés Application Programming Interface – Interfaz de Programación de Aplicaciones) es el conjunto de funciones y procedimientos (o métodos si se refiere a programación orientada a objetos) que ofrece cierta librerÃa para ser utilizado por otro software como una capa de abstracción.
Una API representa un interfaz de comunicación entre componentes software. Se trata del conjunto de llamadas a ciertas bibliotecas que ofrecen acceso a ciertos servicios desde los procesos y representa un método para conseguir abstracción en la programación, generalmente (aunque no necesariamente) entre los niveles o capas inferiores y los superiores del software.
Uno de los principales propósitos de una API consiste en proporcionar un conjunto de funciones de uso general, por ejemplo, para dibujar ventanas o iconos en la pantalla. De esta forma, los programadores se benefician de las ventajas de la API haciendo uso de su funcionalidad, evitándose el trabajo de programar todo desde el principio. Las APIs asimismo son abstractas: el software que proporciona una cierta API generalmente es llamado la implementación de esa API. »
Pues bien, sin mas preámbulos, aquà tienes la lista completa de las APIs de la Web 2.0:
Publicidad
| Google AdSense | Advertising management |
| Google AdWords | Search advertising |
| Microsoft adCenter | Online advertising services |
| UrlTrends | Link tracking and search optimization |
| Wordtracker | Search engine optimization services |
| Yahoo Ads | Online ad management |
| Yahoo Search Marketing | Search advertising platform |
| Answerbag | Questions and answers service |
| Blogwise | Blog and feed search service |
| SplogSpot | Database of spam blogs |
Búsqueda de Blogs
| Blogwise | Blog and feed search service |
| SplogSpot | Database of spam blogs |
| Tailrank | Blog search and news aggregation service |
| Technorati | Blog search services |
Blogging
| Akismet | Blog spam prevention service |
| Blogger | Blogging services |
| FeedBlitz | Blogs by email service |
| FeedBurner | Blog promotion tracking service |
| LiveJournal | Blogging software |
| Performancing | Blog management |
| TypePad | Blog management |
| Weblogs | Blog ping service |
| Windows Live Spaces | Blog services |
Marcadores
| Blogmarks | Social bookmarking |
| del.icio.us | Social bookmarking |
| linkaGoGo | Social bookmarking service |
| Ma.gnolia | Social bookmarking service |
| OnlyWire | Social bookmarklet service |
| Shadows | Social bookmarking and community |
| Simpy | Social bookmarking |
Calendararios
| 30 Boxes | Calendar service |
| Google Calendar | Calendar service |
| Spongecell | Online calendar service |
Chat
| AOL Instant Messenger | Instant messaging chat service |
| AOL Presence | Online presence service |
| Google Talk | Chat application |
| IMified | Instant messenger buddy |
| Lingr | Online chatroom services |
| MSN Messenger | Chat and messaging |
| WebAIM | Web based instant messaging |
| Yahoo Messenger | Instant messaging |
Comunidades
| Blue Dot | Content sharing community |
| coRank | Distributed user reviews service |
| Social networking service | |
| PartySpark | Social events service |
| RockYou Super Wall | Content sharing platform within Facebook |
| Community site |
Email
| Email Address Validator | Email address validation service |
| ExactTarget | Email delivery services |
| IntelliContact | Email marketing service |
| JangoMail | Bulk email service |
| Mailbuild | Email forms and templates service |
| Publicaster | Email marketing management |
| StrikeIron Email Verification | Email verification service |
| Vertical Response | Email management services |
| Webmail.us | Email hosting service |
| WhatCounts | Email management services |
| Yahoo Mail | Web based email system |
Empresa
| Employease | On-demand human resource management |
| Google Provisioning | User provisioning for Google Applications |
| Lokad | Time series forecaster |
| NetDocuments | Enterprise document management service |
| NetSuite | Business application suite |
| Salesforce.com | CRM services |
| WebEx | Conferencing and collaboration services |
Eventos
| Eventfinder | Events calendar |
| Eventful | Events discovery and demand |
| Spraci | Events and clubs database |
| Upcoming.org | Collaborative event calendar |
| Zvents | Local events search and community |
Finanzas
| Blinksale | Online invoicing services |
| Currency Rates | Currency rates |
| Dun and Bradstreet Credit Check | Credit check |
| FreshBooks | Online invoicing and time tracking |
| KashFlow | Online accounting software |
| Moneytrackin | Expense tracking |
| NetAccounts | Online accounting service |
| Prosper | Peer-to-peer network |
| StrikeIron Historical Stock Quotes | Stock price quotes for US equities |
| StrikeIron Mutual Funds | Historical mutual funds |
| StrikeIron Stock Quotes Basic | Real-time stock quotes |
| Wesabe | Personal finance management and community |
Gubernamentales
| Cicero | Lookup service for US elected officials by address |
| Civic Footprint | Political geography lookup for Illinois |
| Democracy In Action | Advocacy services for nonprofits |
| FedSpending.org | Database of US government spending |
| Follow The Money | Database of US campaign contributions |
| GovTracker | Rhode Island state data services |
| LOUIS | US federal documents database |
| Open Patent Services | European Patent Office web services |
| Sunlight Labs | US Congress database service |
| TheyWorkForYou | Track the UK Parliament |
| Who is my Representative | Database of US congressional representatives |
Internet
| Alexa Site Thumbnail | Thumbnail images of web site home pages |
| Alexa Top Sites | Web site traffic rankings |
| Amazon EC2 | Elastic Compute Cloud virtual hosting |
| Clicky | Web site analytics |
| Compete | Internet web site metrics and analytics |
| Cordurl | Geo coordinate translation |
| Dapper | Service for API creation |
| Domain Tools | Internet domain name lookup |
| Durl.us | URL shortening |
| Ecommstats | Web analytics |
| Hostip.info | IP lookup |
| HTML2PDF | HTML to PDF conversion |
| Internet Archive | Non-profit Internet library |
| IP Address Lookup | Determine IP address from domain name |
| Mint | Web site metrics and reporting |
| Mon.itor.us | Web site monitoring services |
| MyNotify | Feed publication |
| Nenest | Web forms and application framework |
| Outune | Web map engine |
| Pingdom | Web site monitoring and reporting |
| Qurl | URL redirection |
| SoftLayer | Systems management and monitoring |
| UnAPI | Proposal for web clipboard |
| W3Counter | Web site metrics tools |
| Webride | Attaches discussions to any site |
| WebThumb | Thumbnail image generation |
| Windows Live Custom Domains | Web site administration |
| Yahoo Site Explorer | Web site analysis service |
Búsqueda de empleo
| Indeed | Job search services |
| SmashFly | Job board posting service |
Mapas
| ArcWeb | Mapping and GIS services |
| BigTribe | Location based advertising |
| deCarta | Location-based services |
| EarthTools | Web services for geographical information |
| FeedMap | Blog geo-coding |
| Garmin MotionBased | GPS services and mapping |
| geocoder | Geocoding services for US |
| geocoder.ca | Geocoding services for Canada |
| GeoIQ | Geospatial analysis and heat mapping service |
| GeoNames | Geographic name and postal code lookup |
| GetMapping | Aerial photography and mapping service |
| GlobeXplorer | Mapping services |
| Google Maps | Mapping services |
| HopStop | Mass transit and walking directions |
| iShareMaps On Demand | UK Postcode Geocoder |
| Map24 AJAX API | Mapping services |
| Mappr | Photo mapping |
| MapQuest | Online mapping service |
| Mapstraction | Mapping API abstraction layer |
| MetaCarta | Location and geotagging services |
| Microsoft MapPoint | Mapping services |
| Microsoft Virtual Earth | Mapping services |
| Multimap | Global online mapping service |
| NASA | Satellite mapping images |
| Naver Maps | Korean mapping service |
| Nearby.org.uk | Geocoding service for UK |
| Ontok | Geocode any US address |
| OpenLayers | Mapping API abstraction layer |
| OpenStreetMap | The Free Wiki World Map |
| Platial | Collaborative geographic service |
| Plazes | Location discovery service |
| Poly9 FreeEarth | 3D mapping service |
| Pushpin | Mapping service |
| Urban Mapping | Urban geo-spatial data services |
| USGS Elevation Query Service | Determine elevation based on latitude and longitude |
| ViaMichelin | Mapping, directions, and travel booking |
| Wayfaring | Map creation and sharing service |
| WHERE GPS | Mobile GPS widget platform |
| Where Is Tim Web Service | Location tracking |
| Where2GetIt Geospatial | Non-mapping geospatial services |
| Where2GetIt SlippyMap | Online mapping service |
| Whereis | Australian and New Zealand mapping service |
| Wigle | Wireless network mapping |
| Yahoo Geocoding | Geocoding services |
| Yahoo Map Image | Map image creation service |
| Yahoo Maps | Mapping services |
| ZeeMaps | Embedded maps and international geocoding |
| ZoomIn | Australian mapping service |
Gestión de Medios
| BBC | Multimedia archive database |
| Grouper Video | Video sharing service |
| Orb | Digital media remote access and management |
| Phanfare | Photo and video sharing service |
| Streamload | Online media storage |
Mediciina
| cPath | Medical database lookup |
| Kegg | Bioinformatics data services |
| NCBI Entrez | Life sciences search services |
| SeqHound | Bioinformatics research database |
MensajerÃa
| 411Sync | SMS, WAP, and email messaging |
| Aql | SMS solutions portal |
| Clickatell | SMS Messaging services |
| Jaiku | Social messaging service |
| Mobivity | SMS marketing messaging service |
| Movil | SMS messaging |
| PartySync | Messaging services |
| Sabifoo | IM to RSS conversion service |
| SmsBug | SMS messaging services |
| StrikeIron Global SMS Pro | SMS messaging services |
| StrikeIron Mobile Email | Mobile email messaging service |
| Textamerica | Moblogs |
| Trekmail | Messaging services |
| Twittervision | Location based data for the Twitter service |
| Userplane | Communication software for online communities |
| Vazu | SMS messaging service |
Música
| AOL Music Now | Music playlist management |
| Digital Podcast | Podcast search |
| Faces.com | Photo and media sharing service |
| Feedcache | Feed caching service |
| Freedb / CDDB | Online CD catalog service |
| Last.fm | Music playlist management |
| MP3Tunes | Music services |
| MusicBrainz | Music metadata community service |
| MusicDNS.org | Music fingerprinting service |
| MusicMobs | Social music service |
| OpenStrands | Music recommendation and discovery |
| Rhapsody | Online music services |
| SeeqPod | Music recommendation service |
| SNOCAP | Digital music marketplace |
| Soundtoys | Visual artists works repository |
| Tunelog | Music metadata management |
| WebJay | Music playlist management |
| Winamp | Customizable music player |
| Yahoo Music Engine | Desktop music player |
Noticias
| AmphetaRate | News aggregator |
| ClearForest Semantic Web Services1 | Natural language processing tools |
| Daylife | Online News Service |
| Digg | |
| Findory | Personalized news aggregation |
| Macromedia News Aggregator | Data access service |
| Moreover | News delivery |
| NewsCloud | Social news service |
| NewsIsFree | Online news aggregation |
Oficina
| Backpack | Online information manager |
| Big Contacts | Web based contact management |
| EditGrid | Online spreadsheet |
| Google Documents List | Document management services |
| Google Spreadsheets | Online spreadsheets |
| Numbler | Online spreadsheet service |
| SlideShare | Presentation sharing community |
| Zoho | Online office suite |
Fotos
| AOL Pictures | Online photo management |
| Buzznet | Photo sharing |
| Flickr | Photo sharing service |
| Fotolia | Royalty free stock photos |
| Google Picasa | Photo management and sharing service |
| imageLoop | Animated slideshow service |
| Panoramio | Photo upload site with organizer |
| Pixagogo | Online photo services |
| Riya | Photo search |
| ShutterPoint | Stock photography service |
| Smugmug | Photo sharing service |
| Snipshot | Online photo editing service |
| WebShots | Photo sharing service |
| Yahoo Photos | Online photo service |
| Zoto | Photo sharing service |
Recomendaciones
| Criteo | Distributed recommendation service |
| EasyUtil | Recommendation service |
| RapLeaf | Portable ratings system |
| Yelp | Local user reviews and city guides |
Referencia
| Aonaware Dictionary | Dictionary lookup service/td> |
| City and State by Zip Code | Address lookup service |
| Dun and Bradstreet | Research company background data |
| Bussines Verification | Business research services |
| FUTEF Wikipedia API | Third party Wikipedia web service |
| ISBNdb | Books database |
| Library of Congress SRW | Information database search |
| Microsoft MSDN | Technical reference library |
| OpenDOAR | Academic research repository |
| PhoneVal | Phone number validation service |
| RealEDA Reverse Phone Lookup | Lookup address and name via phone |
| SRC Demographics | Demographic reference data |
| StrikeIron Address Verfication | Global address verification service |
| StrikeIron Do Not Call | Telephone number verification |
| StrikeIron Insider Trading | Insider trading transaction information |
| StrikeIron Phone Number Enhancement | Adds address and statistical data based on phone number |
| StrikeIron Residential Lookup | Residential directory lookup and validation service |
| StrikeIron Reverse Phone Lookup | Reverse phone lookup services |
| StrikeIron Sales Tax Basic | Sales and use tax data service |
| StrikeIron Super Data Pack | APIs for variety of reference data sources |
| StrikeIron US Census | Census data information service |
| StrikeIron Zacks Company Profile | Corporate profiles web service |
| Talis | Library 2.0 reference services |
| UrbanDictionary | Slang dictionary lookup |
| US Yellow Pages | Telephone directory |
| Yahoo Answers | Community driven reference service |
Búsqueda
| Alexa Web Information Service | Web site information and traffic data |
| Alexa Web Search | Web Search Engine |
| Amazon A9 OpenSearch | |
| Gigablast | |
| Google Ajax Search | Web search components |
| Google Code Search | Code search service |
| Google Desktop | Desktop search and gadgets |
| Google Search | Search services |
| Kratia | Democratic search engine |
| Naver | Korean search engine |
| Vast | Structured web search |
| Windows Live Search | Internet search |
| Wink | Social search service |
| Yahoo Image Search | Image search services |
| Yahoo Local Search | Local search service |
| Yahoo My Web Search | Personalized search services |
| Yahoo Related Suggestions | Search suggestion service |
| Yahoo Search | Search services |
| Yahoo Term Extraction | Contextual search service |
| AOL Open Auth | Authentication services |
Compras
| Amazon eCommerce | Online retailer |
| Amazon Historical Pricing | Historical product sales data |
| Authorize.Net | Internet based payment gateway services |
| AvantLink | Affiliate marketing network |
| CNET | Shopping services |
| Commission Junction | Online affiliate programs |
| DataUnison eBay Research | eBay pricing and sales trend data |
| Direct Textbook | Book price comparison service |
| eBay | Online auction marketplace |
| GoodStorm | Online retail ecommerce |
| Google Base | Platform for structure and semi-structured data |
| Google Checkout | Shopping cart services |
| PriceRunner | Shopping comparison engine |
| Shopping.com | Online retail shopping |
| SwapThing | Community driven swapping site |
| UPC Database | UPC lookup service |
| Windows Live Expo | Online classifieds service |
| Yahoo Shopping | Shopping services |
| Zazzle | On-demand product creation service |
Almacenamiento
| Amazon S3 | Online storage services |
| Box.net | Online file storage |
| MoveDigital | File delivery and management services |
| Omnidrive | Online storage services |
| Open Xdrive | Online data storage service |
| Openomy | Online file system |
| Tagalag | Email tagging |
| TagFinder | Tag extraction service |
| Tagthe.net | Tag recommendation service |
| TagTooga | Tag based Internet directory |
Video
| Truveo | Video search |
| Blinkx | Video search |
| Dave.TV | Video distribution network |
| LiveVideo | Video repository and user community |
| Revver | Video services |
| Veoh | Virtual television and video network |
| Video Detective | Film trailers, cast, images, and related information |
| Yahoo Video Search | Video search |
| YouTube | Video sharing and search |
Widgets
| ClearSpring | Widget creation, distribution, and tracking services |
| Google Gadgets | |
| Netvibes | Personalized home page with widgets |
| Pageflakes | Personalized start page and widgets |
| Serence Klip | Desktop gadgets |
| SpringWidgets | Widget platform |
| TagWorld | Social web services |
| Windows Live Gadgets | Online gadgets service |
| Windows Sidebar Gadgets | Desktop gadgets |
| Yahoo Widgets | Desktop widgets |
| Yourminis | Personalized start page |
WIKI
| DBpedia | Structured query interface to Wikipedia |
| JotSpot | Wiki-style collaboration tools |
| PBwiki | Consumer wiki farm |
| WikiMatrix | Wiki search and comparison service |
VÃa | FunGarden
