Day 30: Rarest RPG Owned
I don't own any rare RPGs, only common ones and a load of PDFs (inherently not-rare). By that argument, the answer is either:
Hellcats and Hockeysticks, because the least common RPG must be the rarest; or
one of the ones I'm writing myself, because nobody else owns them. Technically this would be De Jure, the only one that I think is arguably complete, although it's more a hack than a game per se.