Mimi and Toutou Go Forth is a set of simple naval rules for WWI naval battles on Lake Tanganyika. Obscure, to be sure, but intriguing.
Don offers an updated version of his air combat rules, which he now calls Aerial Craps.
Orks and Dwarves in a WWI setting? Sure. Here’s a set of fantasy WWI Rules.
Roundwood’s World has some great photos of his WWI wooded terrain board.
Roundwood’s World has a nice post on how he modeled a marsh board for his WWI games.