Marc Andreessen has an interesting post in which he attempts to catagorize internet platforms into three levels:

* A Level 1 platform’s apps run elsewhere, and calls into the platform via a web services API to draw on data and services — this is how Flickr does it.

* A Level 2 platform’s apps run elsewhere, but inject functionality into the platform via a plug-in API — this is how Facebook does it.

* A Level 3 platform’s apps run inside the platform itself — the platform provides the “runtime environment” within which the app’s code runs.

The attempt at catagorization is thought provoking, but has at least one oddity - Ning ends up in the same catagory as EC2/S3 and by extension AppLogic. IMHO this actually seems to call for a fourth level. I’m not sure whether I’d classify AppLogic as level 4 or level 2.5 based on Marc’s requirements, but you can read his post and decide for yourself.