We put data and information into individual websites like facebook, linkedin, basecamp, salesforce, twitter, wordpress, etc. The more web services emerge and the more information each web service hosts, the harder it becomes for 2 websites to ‘talk to’ each other. That is why so many successful websites have APIs.

Think about it this way. You are a member of facebook, linkedin, flickr, etsy, and ebay. When you post a product on etsy.com can you invite your contacts from facebook to buy your products, and can you add a link to your etsy store in linkedin? Can you post an auction on ebay for your etsy products? If the answer is yes, that is because each website has its own set of extensible API’s for exchanging data objects with other websites.

The Google Maps API lets other websites (like mapvivo.com) put a google map into their website, and ‘move their data around’ on the map. So if you are a website and you have data such as users, places, events, etc- you can put that data into another web application.

http://www.programmableweb.com/apilist

Some web applications only exist because of API’s. Those are called ‘Mashups’- and there are many of them.

http://www.programmableweb.com/popular/recent

Personally, I think the growth of API’s will lead to another interesting web 3.0 concept. Previously, people put data into websites. Now, websites have API’s so other websites can pull and exchange data. Eventually, the internet will act more like facebook as a platform and database for 3rd party applications. In other words. your personal or business data will be hosted in one standardized data cloud. You will give permission to 3rd party apps (facebook, salesforce, calendar, etc) to pull your data out of one data cloud into its application. This will allow 3rd party apps to be built and deployed as easily as facebook apps or iphone apps. Conversely, Microsoft might just gain hegemony and out-compete every 3rd party app.