Is a DLL developed in .NET is accessible from any language or operating system?

I am creating a DLL that I want to distribute to public to use it the way they want. This DLL contains common utility functions. People can use it on any operating system and with any language or framework. So, I want to ask that the DLL created using .NET 3.5 or above is accessible from other languages, operating systems or frameworks? Or do I need to write these functions in other language too or for different operating systems? I know only C# and I don't want to spend money for a free publicly distributed library.