Here are some interesting thoughts on playing Song of Blade and Heroes solo.
Isuldur’s Bane is the name of a free set of rules for playing Games Workshop’s Lord of the Rings Battle Game.
Three Plains is a free fantasy wargaming system. It also comes with free print-and-play figures.
Brutality is a miniatures agnostic skirmish wargame set in a science fantasy realm. You can get a free version at the link.
Red Dragon Inn: Battle for Greyport is a neat deckbuilder published by Slugfest Games. You can get a print and play version at this link.