Hmm. The most obscure ones in my collection:
Behind Enemy Lines - WWII roleplaying.
Expendables - a scifi RPG I got almost 20 years ago. PCs are scouts working for a corporation that runs everything in human space. The characters go to planets that are potential new colonies or which might have valuable resources, and explore them. Generally, they are given specific missions. It's a fairly short book, and looks like it'd be fun to play. Never got a chance to run it. I may have to scare up some players for it, though.
Rus - an Australian RPG that is set in a mythical/legendary Russia. I even have an adventure for it. Not a very inspiring book, unfortunately, so I was never motivated to run it.
I do have a copy of the "Kulp Edition" of Spawn of Fashan, though I wouldn't say it's all that obscure.