A "platform" is a system that can be programmed and therefore customized by outside developers -- users -- and in that way, adapted to countless needs and niches that the platform's original developers could not have possibly contemplated, much less had time to accommodate.
- A Level 1 platform's apps run elsewhere, and call 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. Most likely, a Level 2 platform's apps also call into the platform via a web services API to draw on data and services.
- A Level 3 platform's apps run inside the platform itself -- the platform provides the "runtime environment" within which the app's code runs.
- Akamai's EdgeComputing
- Amazon S3, EC2 and FPS
- Ning (Marc's own company)
- Google Apps could became a level 3 platform
- Second Life