the whole list of rail guns, coil guns and the like. These use electromagnets to shoot projectiles (most often metal) at velocities ranging similar to a .22 and up to 7,000 mph. DIY kits abound. I've even seen them up to 300 rounds per second.
Combine these with off the shelf and diy high res cameras, facial tracking, camera targeting, and EMP (electronics killers)... I think the DIY crowd will soon outpace the oppressors. Should be interesting.