GCC

GCC screenshots

GCC was originally written as the compiler for the GNU operating system
Main window
GCC 4.7 : Main window

Alternative downloads

WinAVR
WinAVR includes avr-gcc , avrdude (programmer), avr-gdb (debugger), and more!
FREE
GCC - Open Source Compiler for MSP430 Microcontrollers
Debugger and open source C/C++ compiler for MSP430 microcontrollers.
4.1.0.0
FREE
Hitex Development Tools GNU C/C++ Tools for ARM
GCC is a set of compilers produced for various programming languages.
4.03.0003.1
FREE