Does .net can run other kind of platforms?

You don't really understand what .NET is.

Please read: http://en.wikipedia.org/wiki/.NET_Framework[^].

Now, .NET is based on CLR, which is standardized under ECMA and ISO. See http://en.wikipedia.org/wiki/Common_Language_Runtime[^].

There is a number of alternative implementations of CLR; most advanced of them is Mono, available in many platforms:
http://en.wikipedia.org/wiki/Mono_software[^],
http://www.mono-project.com/Main_Page[^].

Using Mono, you can develop software and even Forms applications on Windows and run them without recompilation on Linux, Mac OS X, etc.

Also, there are Portable.NET and (umbrella) DotGNU alternatives, see:
http://en.wikipedia.org/wiki/Portable.NET[^],
http://en.wikipedia.org/wiki/DotGNU[^].

Besides, there are operating systems based on CLR, mostly under development:

To get an idea of how managed CLR platform can be used in development of OS, please read about the following projects:

Cosmos:
http://en.wikipedia.org/wiki/Cosmos_%28operating_system%29[^],
http://cosmos.codeplex.com/[^];

SharpOS:
http://en.wikipedia.org/wiki/SharpOS_%28operating_system%29[^],
http://www.sharpos.org/[^];

ETH Zurich — Microsoft Research Barrelfish:
http://en.wikipedia.org/wiki/Barrelfish[^],
http://www.barrelfish.org/[^].

Microsoft Midori (code name):
http://en.wikipedia.org/wiki/Midori_%28operating_system%29[^].