Warzone Modern battles is a set of free modern Wargaming rules for 1:72 or 20mm Squad/Platoon games.
Andrew Stevenson offers new set of modern wargames rules based on the Lightning War/Red Storm system. Called “By Fire and Movement”, it is aimed at playing a corps or more each side. You can get the free beta version by joining the Yahoo Group.
PZ8 1950-69 is a set of free wargames rules for using 6mm miniatures to refight battles of the mid to late 20th century. They’re at the 6mm Miniatures Yahoo Group.
Counterterrorist Force is a set of free wargames rules for gaming modern counter terrorist operations. The author writes:
CTF (Counter-Terrorist Force) is a pure “player vs. player” (1 on 1) game where the main focus is on tactics and realistic combat. The game is played from both sides of the conflict. One person plays the terrorists and the other takes the role of counterterrorist. Not only do you execute missions, you also run your own counter terrorist corporation and try to work your way up from scratch. You will also fight occasionally as a terrorist so that your friends can play as counter terrorist troopers too. Game play can either be single missions to improve your corporation, or otherwise in campaign mode where two campaigns are interwoven – you and your opponent take turns as terrorists – and you both have your own counterterrorist unit to run every second game in your individual campaign.
Jihad is Stan Johansen’s rules for modern insurgencies. There also are printable action cards and counters.