"Electromagnetic pulse grenades damaging to electronic equipment."
EMP grenades are ranged weapons can stun mechanoids, turrets, mortars, and deplete shield belts, but do not deal physical damage. A target that is stunned shows a mote saying 'STUN'. After being stunned, targets may randomly become 'Adapted' and gain stun immunity. This stun immunity is not permanent, but takes a long time to wear off (usually lasts longer than the fight that caused it).
They can be crafted, purchased or looted from dead raiders.
Using EMP grenades against friendlies counts as an attack even if they aren't hurt.
EMP grenades are very effective against centipedes. Their slow move speed and large size make them easy targets. They have a very high damage potential, so even temporarily shutting them down will give your colonists an advantage in a battle.
It is a good idea to manually aim EMP grenades instead of letting your colonists do that. They will not lead the targets and will not attack targets which can only be hit by area of effect. Repeated applications while the target is already stunned will cause stun adaptation to happen earlier, while not affecting stun time significantly.