Where exactly can I find open source C# code to study? Can you name me some open source applications based on C#?

Most of the open source software out there that I have found so far has been programmed in some other language -popular being c++, java for openoffice etc. etc. and I am unable to find any open source software built on C#.I have learned C# and would like to lend a hand to open source projects if there are any products on C# code so that I can study as well as help out as part of the open source community....I looked into C++ code and found it rather confusing as I am not completely aware of it's syntax's so please if you are aware of any C# based open source projects do let me know.I also wanted to know that if I along with my team convert a particular open source project code based in some other language to C# for e.g. convert Java Code,C++ Code,Python Code to C# Code and release it,would it be considered modification as the code would be from a different language even though the product would be invariably the same?