This has been around for a long long time now so it's super mature, and it's very cool! I've used it in the past to make some esoteric keyboard adapter. You ca

This has been around for a long long time now so it's super mature, and it's very cool! I've used it in the past to make some esoteric keyboard adapter. You can do a lot with it, but you may run up against a ceiling once you've committed an AVR to V-USB use as the timing requirements even at low bit rates are very strict, and you might want to consider AVRs with built-in USB transceivers if this becomes limiting.