OpenModularTurrets is a mod that adds craftable low, medium and high level turrets. These turrets need to be powered with RF (Redstone Flux) to work. Each tier of turrets requires higher levels of energy per shot. The low level turrets shoot things like rocks, while higher level turrets shoot things like explosives and lasers. Each turret has to be positioned on a turret base of a corresponding level. The base is where you feed the electricity and store the ammunition as well as where you can configure the turrets.  Each turret can be set to attack only hostile mobs, all mobs and all mobs and players. You can also add trusted players to your turrets for a multiplayer base.