OSRIC (Old School Reference & Index Compilation) offers a free fantasy role playing game inspired by first edition Dungeons and Dragons. It’s not the first effort I’ve seen trying to recapture the magic of 1st edition, before the life was sucked out of it with the bloated later editions.
The Farland Mass Combat System is designed to help role players resolve large scale conflicts. There’s also a great — and free — program to help you do so.
I recently played this semi-role playing game with my AP Political Science students and we all enjoyed it very much. In Executive Decision, the players each take on the role of a member of the president’s cabinet and try to promote their agenda as critical events unfold in real time. Highly recommended.
Edgar Rice Burroughs’ Barsoom novels are among my favorite guilty pleasures. Sean K. Reynolds has a page with material, including monster and character profiles from his d20 Barsoon campaign.