Steve Jones offers his Paintingshed Napoleonic Rules. The rules are written for 6mm figures.
The Miniature Wargaming Editor
Modeling Farm Fields
From the Terrain Tutor comes another excellent video. This one is on making farm fields for your wargames table.
Top Skirmish Games
There’s an interesting thread on Reddit detailing top miniature skirmish games. Most are obviously not free, but the threat is a good read.
Solar Scourge Science Fiction Rules
Solar Scourge is a set of free wargames rules designed for 6mm science fiction miniatures.
Corvet: Skirmish Starship Combat
Corvet is a free skirmish game of starship combat for two or more players. What makes it different is that it tries to implement a “captain’s-eye view of your ships”