One Turret, Any Ammo. (bullets, flamethrowers, rockets, cannons, railguns, shotguns, capsules/grenades)
Mods introducing new content into the game.
New ways to deal with enemies, be it attack or defense.
When you say "friendly fire free" you mean the railgun won't obliterate every building in his path and the rocket blasts wont destroy my stuff on its blast radius?