HALO Combat Miniatures Evolved is a set of free wargames rules based on the HALO science fiction franchise.
Three Musketeers Legends of the Old West Variant
Sgt. Perry’s Heroes offers a variant of the Legends of the Old West rules for miniature wargames set in the era of the Three Musketeers.
Paintingshed Napoleonic Rules
Steve Jones offers his Paintingshed Napoleonic Rules. The rules are written for 6mm figures.
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.