Autobombs... They seem pretty useless in most respects. They're definitely useful, but havingg to keep a steady supply of them to the system being attacked. Ever thought of them as a continuous stream of death to invaders?
Simply put, two Space Docks set to loop a production cue of nothing but Autobombs. Set the Space Docks on aggressive, and whenever you get a wave of several hundred ships to the planet this defensive setup is being deployed on, it is quite a sight to behold and laugh hysterically at. Obviously, there's only so much these can protect against, but a swarm of suicidal ships racing towards your enemies is enough to ward them off somewhat.
I just used this as a last-minute tactic in one of the phases of the "Fallen Spire" campaign. One of my systems had about 500 AI ships entering it, and I had minimal defenses. This combination of Mark I-III Autobombs saved the system singlehandedly.