Warstuff is a set of one page rules for playing games with whatever you have in your box. The author writes:
WarStuff is a single-paged ruleset designed to be played with any miniatures or toys you have at hand. The rules are perfect as an introduction to wargaming for kids, and for conventions and pick-up games where players might have models from different lines.
The Wargaming Depot blog has a tutorial on making terrain tiles from cork.
It’s an idea that I considered for quite some time, before finally settling on doing a similar thing with 1 foot square carpet tiles.
RPG Now has a free horror RPG module called Dead of Night: Night of the Santa Claws. It’s designed for the Dead of Night RPG, but no doubt could be modded for any other system.
The Perfect Captain has released a campaign system for his Red Actions! rules set. From the Captain:
We have completely outdone ourselves this time! What if I told you this was a campaign game that takes maybe 30 minutes to create from scratch, with limitless scenarios, a different map each and every time, and has counters representing the following armies and their equipment: Reds (All over Russia), Whites (Kolchak, Deniken, Wrangel, Yudenich, Komuch, Kappelites etc), Greens (Mahknovists), Estonians, Latvians, Finns, Lithuanians, Ukrainians, Poles, Armenians, Turks, French, Greeks, Japanese, American, British Empire (Including Canadians, Australians, and Indians), and Freikorps.