If you can program it, then it's a platform. If you can't, then it's not.Level 1 represents REST and SOAP API's , where the core system is outside the API. Marc calls this the "Access API". The barriers to entry for app developers are high, because it requires a lot of technical expertise, IT infrastructure and financial resources to create, maintain and scale an app on the Level 2 platform.
Level 2 Marc describes as "Plug-In API". Facebook represents a Level 2 API. The developer creates an app which users can plug in into their Facebook profile. As with Level 1, the core system of the app lives outside of the platform, e.g. Facebook apps are hosted on the developer's server and not on Facebook's server farm. While applications running on the Level 2 platform are easier to build than applications for the Level 1 platform, it is much more difficult to build the platform itself.
Now comes the most interesting part, Level 3, what Marc calls "Runtime Environment". Everything lives inside the platform. Developers don't need to run their own servers anymore, they just upload their code to the platform. And again, it is getting more difficult to build the platform, but easier to build the apps running on that platform. Examples for Level 3 platforms are Ning, SalesForce and SecondLife.
And Marc says:
I believe that in the long run, all credible large-scale Internet companies will provide Level 3 platforms.and it goes on and on, huge post, but really worth reading it and now I know how the thing I am secretly working on is called ...