cc65 is a complete cross development package for 65(C)02 systems, including a powerful macro assembler, a C compiler, linker, librarian and several other tools.
cc65 has C and runtime library support for many of the old 6502 machines, including: Commodore VIC20, C16, C116, Plus/4, C64, C128, CBM 500/600/700, GEOS C64/128, Apple 2, Atari 8 bit, Lynx, Nintendo Entertainment System (NES), Supervision console, Oric Atmos.