Day 15 - Which RPG do you enjoy adapting the most?
This is a tough one, since I'm not sure I actually understand the question.
In the case of adapting something into an rpg, I would have to say that I rather enjoy adapting the Mark Schultz Xenozoic Tales (aka Cadillacs & Dinosaurs) to a roleplaying game set of rules, since I don't really like the GDW game that came out. There are also a couple of other game concepts, mostly from novels, that I'd love to adapt but there just isn't time and all that.
If you're thinking of adapting material into a pre-existing rpg, I would have to say that it's been fun adapting material from the Arabian Nights stories into the Coriolis - The Third Horizon RPG, as that's been a good challenge. I'm also looking forward to adapting some of the Scandinavian myths and legends into the Trudvang Chronicles RPG when that game comes out.
(Note: This is the last entry that I'll be making for the month until I get back from GenCon 2017, at which time I'll be playing at least a week of catch-up.)