Double Tap is a set of free wargames rules for games involving special operations forces in the near future. The rules are just one page, but look as though they are anything but simplistic, as they use a reaction system.
Grunts, Leathernecks and Charlie is a set of free wargames rules set in the Vietnam War. The author writes:
Players who are interested in a FUN and FAST Vietnam game system can consider these rules a flexible framework for use. I designed these rules to be used by both beginners and veteran players. Play can be quick and easy OR made more realistic and slower by adding advanced options. If you do not trust your opponents, then this is not the right rules’ set to use. It will assist any player who has an interesting scenario to run at a convention or at a local shop. The Combat systems reflect volume of fire into a specific area combined with the maneuvers of combat units.
From Deep Fried Happy Mice come a set of free wargames rules called Medals of Valor. The Mice write:
Medals of Valor is our system for recreating skirmish and tactical combat during the 20th Century. These are low intensity rules designed for fast play and fun. We have tried to maintain a feel for realism while understanding that a comprehensive detailed system would be very slow and cumbersome. In order to achieve this balance several aspects of tactical combat have been generalized or even in some cases ignored. The system requires that castings be mounted on individual bases. This system uses an extended period of time for a turn which allows for the completion of an action. For example acts of reloading and changing positions as needed can be completed within a game turn. Moves are considered to be a change of position (standing), moving (running) and assuming a defensive position (kneeling). Firing distances are extensive considering the small scale. Soldiers are armed with the weapon with which they are cast. Extra castings should be available for weapon exchanges and casualties.