A free C, C++ and Fortran IDE
A reverse engineering suite (decompiler, editor, debugger and more)
Rapid applications development tool and libraries for FPC
A native Windows port of the GNU Compiler Collection (GCC)
Homebrew toolchains for wii, gamecube, 3ds, ds, gba, gp32 and psp
C library, that logs memory changes made by malloc and free.
Superseded by http://www.ti.com/tool/msp430-gcc-opensource
zCOBOL portable mainframe COBOL compiler, part of the z390 project