OP didn't mentioned complexity, nor any kind of comparison.

Nice then. OTOH, CP/M 2.2 has been open sourced, but I think there are no libre assemblers for it.

Cross-assemblers, there's one: http://john.ccac.rwth-aachen.de:8000/as/ but it's tedious to build under OpenBSD.

As for software, the ZMachine and V3 games don't count as 'libre examples'.