Steve Jackson Games has made the rules for the Classic Car Wars game free for the downloading.
I played the heck out of that game back in the day.
Board Games
Two Flags One Nation Board Game Rules
Two Flags One Nation are a set of rules for do-it-yourself American Civil War board games. The author explains how he generates maps and block pieces with his computer.
Elementum Dueling Mages Card Game
Elementum is a free print-and-play card game ..
of two mages casting elements on each other to win a duel. You and your opponent keep a hand of 5 elements and a Kill card, and each turn you choose 3 of these cards to play into 2 offensive and 1 defensive slot. Each of you keeps track of your active elements using a simple map of interactions and nullifications.
Your goal is to defeat the other mage by resolving a kill card while your opponent has at least 1 active interaction on them or by activating all 5 of their elements at once.
Agent Decker Card Game
Agent Decker is a print-and-play card game with a spy / espionage theme. The author writes:
AGENT DECKER is a mission-based deckbuilding game for one player where you’ll acquire gear and skills by facing obstacles. The alarm raises every turn, so you must pick who you take out. Do you go for the cool weapon, or take out the security camera?
Cardbots :Print-And-Play Card Game
Cardbots is a print-and-play game where you build your robots and then fight with them.