CASM

CASM is a portable (it shouldn't be using anything more than ANSI/ISO features) macro cross-assembler in C. It currently supports the following processors:

• Z80
• 6502
• Gameboy Z80 derivative
• 65c816 (the CPU used in the SNES)
• SPC700 (the CPU used for sound in the SNES)

It can also produce output in the following formats:

• Raw binary (works well for Atari VCS images)
• Spectrum TAP file
• Commodore T64 tape file
• ZX81 P file
• Gameboy ROM
• SNES ROM
• A simple library format for larger projects.
• NES ROM

Source for V1.6 are available here. Sources for the lastest development version are available here.