A native Windows port of the GNU Compiler Collection (GCC)
MinGW: A native Windows port of the GNU Compiler Collection (GCC), with freely distributable import libraries and header files for building native Windows applications; includes extensions to the MSVC runtime to support C99 functionality. All of MinGW's software will execute on the 64bit Windows platforms.
AVR-Eclipse is a plugin for the Eclipse IDE which adds toolchain support, through CDT, for the gcccompiler for the Atmel AVR series of microcontrollers, and adds a toolbar button to allow quick upload of produced code to a target device.