clang
Clang is a popular compiler for C, C++, Objective-C and Objective-C++ languages. It compiles code down to LLVM, and then uses the LLVM framework to convert this into machine code (in this respect, Clang can be thought of as a compiler frontend).
History
The Clang compiler was open-sourced by Apple in July 2007, after they created it as a front-end to LLVM.