Doomsday Machine a multi-weapon tower. Built by all T2 land/air cons it packs three types of laser turrets that can aim and shoot independently.
First, the tachyon accelerator for long-range highly damaging outbursts.
Secondly, a high energy laser turret for mid-range.
Finally, a double light laser turret for short range anti-swarm purposes. It can deal with most T2 units and even light T3.
When swithed off if hides its turrets under heavy armor. Use it to soak big amounts of damage when targeted, while your other defensive structures do all the work.