MINIMON is a Machine Language Monitor for the Commodore VIC-20.
It is a combined hardware/software project: a cartridge for the computer's expansion port (with a cartridge extender for a secondary cartridge), plus firmware, which is the actual MINIMON monitor.
MINIMON features all commands usually expected from a debugger/monitor: Memory dump and edit, Register dump and edit, Execute code from monitor, Direct Assembler and Disassembler (all documented opcodes of the NMOS 6502), Transfer...