Code::Blocks The open source, cross platform, free C++ IDE.
CodeLite IDE A Cross Platform Open Source C/C++ IDE.
Pelles C is a complete development kit for Windows and Windows Mobile. It contains among other things an optimizing C compiler, a macro assembler, a linker, a resource compiler, a message compiler, a make utility and install builders for both Windows and Windows Mobile.
Orwell Dev-C++ The main site of the 2011 Dev-C++ fork.
SharpDevelop The Open Source Development Environment for .NET.