I want to know the operating systems the .NET works on.

It was initially released for only the Windows platform. The Microsoft provided full framework is still targeted only at Windows. I say "full" because there are now some variations that run elsewhere. Silverlight is a subset of the .NET 3.0 framework and it targeted to run on several prominent OSes (Windows, Mac, Linux).

There is an open source project, the Mono Project which promises to run .NET on many different platforms.

-Peter
compiledthoughts.com

Thanks for giving me the information. Peter, i want to know that microsoft allows to change or modify the .NET framework to b run on multiple platforms

While the runtime free to download and install, the source code for the framework is not open source so you would be hard pressed to be able to get it to run on a non-Windows platform. The framework is designed significantly around the knowledge of the operating system on which it runs (Windows). Simply porting it to a non-windows OS is hardly trivial. If you can do it, Microsoft will probably hire you.

-Peter
compiledthoughts.com

Actually, if he could do the porting, he's way too late to get hired for that. MS started that several years ago, but their biggest supporter (unnamed, and I don't know who it was) pulled the funding and that's why Mono is not an MS group.

Had a couple of friends involved in that when MS was doing it, including my ex-boss who was a mucky-muck in the group. They've all scattered to other groups at MS or have left the company.