Sheep War Online is described as 'turn-based game that can be played solo or against other real players'. There are four games similar to Sheep War Online for a variety of platforms, including iPad, iPhone, Mac, Windows and Xbox. The best alternative is Worms. It's not free, so if you're looking for a free alternative, you could try Hedgewars or Pocket Tanks.
Worms is a series of artillery strategy computer games developed by British company Team17. Players control a small platoon of worms across a deformable landscape, battling other computer- or player-controlled teams. Represent entire series of Worms games.
Duel of Tanks is a turn-based strategic artillery game primarily focusing on multiplayer PVP elements. Demolish players from all around the globe with a huge collection of upgradable weapons in one of the unique battle arenas.