The One Page Fantasy rules are designed as a simpler alternative to Warhammer Fantasy Battle.
Miniatures Rules
Panzer Clash Print-and-Play Card Game
Panzer Clash is a free print-and-play card game with a World War II theme for 2-4 players. From the BGG decription:
Pick a side, either Axis or Allies, and build a deck of 40 cards out of a pool of 100 different cards in order to defeat your enemey.
The deck or Supply contains Factories, Units, Events and Terrain Modifiers. Factories are needed to build Units and Terrain Modifiers as well as to power Events. Units and Events, which usually belong to one or more of the four factions (Germans, Japanese, Americans and Soviets) are used to attack and deal damage to the opponent, have certain beneficial effects on the game or are used to weaken the opponent. For each point of damage a Player receives through Units and Events, he or she puts one card from his or her Supply (deck) onto his or her Junkyard (discard-pile). Is a player unable to draw a card from the Supply, he or she loses immediately.
Far Trek RPG
Far Trek is an RPG set in the Star Trek Universe. It’s one I’d love to play.
There are also paper figures for away teams and aliens.
One Page Kill Team
One Page Kill Team is a set of free science fiction rules for small skirmishes. The authors write:
One Page Kill Team is a single-page ruleset designed to be fast to learn and simple to play. It is a great way to play with just a handful of miniatures and experience heroic skirmishes in a short time.
– Updated January 2015
Chivalry — Old School Games Workshop Magazine Game
Realms of Chaos Blog has a posting about the old GW game called Chivalry, which appeared in an issue of White Dwarf. All the relevant pages there are posted, so you can recreate this classic on your own. It’s a card system for combat between knights.