I published a couple of game hacks for the Acoustic Cover Jam this week, both of which started out on this blog. You can find my conversion notes for Numenera using Into the Odd as well as World of Ultraviolet Grasslands there.
Troika! is a science fantasy OSR game with some really cool ideas in it. Several of them you could pull out and put in your own game even if you don't play Troika! per se. Here are four of them.