The Barons of Fyn is a free downloadable card and tile game from Bones Games. In the game, rival barons try to expand their borders, building a fiefdom of loyal towns and cities, and strengthening their armies. It’s beer and pretzels for 2 to 6 players. I’ve played this, and its fun.
Floating Islands is a free print and play game about building an archipelago from floating sky islands.
Lou Coatney offers Stalingrad Attacked, a free, complete board wargame. Coatney is a veteran game designer with a number of published designs, including Dark Crusade.
Cannonade is a Napoleonic era board style wargame designed to be played on a hex board. While the board isn’t provided, the game does include counters for you to print out.
Invisible City Games offers a free board game called Aliens vs Cows. The aliens try to abduct cows. The cows try to protect the planet from the invasion.