There's a lot of discussions right now about "platforms" on the Internet.  Think about giving your web site the ability to talk with others and allowing users to manipulate content to do things you couldn't imagine.

Marc Andressen says there are three types of platforms - from the simple ability to access information (Flickr, Del.icio.us) to platforms that are the applications (Salesforce.com, Ning).  Facebook, with Facebook apps, would be somewhere inbetween.  Fred Wilson believes that all great products are platforms - and notes that his portfolio company Twitter get's 10X the traffic volume from it's API (platform interface) versus their twitter.com website.

The image above is an interesting example of how you can combine different "platforms" to create something new (from Swissmiss via Core77).  Adobe's CS3 (Illustrator, Photoshop, etc.) has the ability to aggregate tips on how to use it's products via Del.icio.us and play those back to you - inside the relevant product (the tool's called knowhow).

Why's this interesting?  Well, CS3 has a platform element: you can add-in your own plug-ins.  And they're accessing Del.icio.us' content via Del.icio.us' API.  In other words, you've got two platforms talking to each other to provide a new, personalized service for end users.