The Black Hack is a stripped-down game designed around first edition D&D, and The Cthulhu Hack… does the same for Call of Cthulhu, although it uses the same mechanics as The Black Hack. What strikes me about both is how plug-and-play they are, and I don’t mean that as a criticism. I think that you could probably run a game in either with nearly no prep time; they seems almost designed for impromptu convention games*. Check them out.
Moe Lane
*Sorry if that sounds pompous; but ‘pickup con games’ sounded like I was describing something… darker.