I really liked Xbattle, but seemed pretty dated, and at least when I played required players to xhost + the server, which back then wasn't that unusual.

There was a similar game, written in java (server and client I believe), called Europa. Had a grid of X's, simple UI (tell units where to go) and the "water pressure" would slow from the cities that make armies to wherever you pointed them. Even included things like using 3 armies to make 1 paratrooper that could jump a square or two.

The author even sent me a copy, not sure I still have it though.