HardMPU is ab0tj's port of SoftMPU onto an arduino microcontroller and interfaced to the ISA bus, which in use behaves just the same as a real MPU401 without needing additional drivers. In my experience it works well for intelligent MIDI output, but it's not a full MPU401 because it's primarily an output device, which for me is just fine. I built a couple of HardMPU cards for myself last year and I think they work really well.
It's open source so you can make your own card for non-commercial use potentially. That's a lot of work but I found it fun and quite educational. I don't think ab0tj has any cards up for sale right now though.
The PC-MIDI card is a re-production of a full MPU401 compatible card. MusicQuest made an MPU401 card and the PC-MIDI card is a reproduction of that, but with some slight improvements like wavetable header and simplified design. I haven't had a chance to try this but it's a more complete implementation with MIDI input and precise timing stuff. The PC-MIDI card's only available as a full product as far as I'm aware, but it was developed on this forum by keropi.
For playing games that use intelligent MIDI, both cards do the same thing 😀