I’ve added TSR’s old WARRIORS OF MARS rpg/skirmish game/sourcebook for Edgar Rice Burroughs’ Barsoom stories. Warriors of Barsoom was written by Gary Gygax and Brian Blume in 1974. I found the PDF for this game, quite by accident, on Archive.org, so I’m assuming the original owners have no concerns about free distribution, but will gladly take it down if TSR/Wizards/Hasbro squawks about it. Somehow I don’t think they’ll get all that upset about it. There’s an EPUB version on Archive as well, but it’s pretty bad– clearly someone ran a conversion script and didn’t clean up the file afterward. I pretty much had to recreate it from scratch, which was a chore! Visit the digital rules page if you are interested.