Disclaimer:
This is a fun thread.
Back in the day the German translation team of the boardgame Space Crusade was worried that by allowing kids to "kill" fictional, plastic monsters in a space ship they would involuntarily turn into murder hobos later in life. Thus we got very creative weapon effects in the German edition.

Lets take a look at them:
Missile Launcher = Holo-Werfer
This weapon would project illusionary foes to confound the aliens in the space hulk. Outnumbered on all sides by those phantasms they would fight them in futile effort until they were exhausted and as a consequence removed from the board.
Assault Cannon/Minigun = Nullzeit-Kanone
This weapon would slow down the aliens in such a way that they no longer posed a threat to anybody in their vicinity. What a way to get removed from the board.
Plasmagun = Black Hole Blaster
This weapon would create a black hole for a short period of time which sucked the aliens into another place/dimension. Unfortunately the writers didn´t realize that being sucked into a black hole would prove fatal for any organism.
LOL!
Lascannon = Time-Twister
This weapon would transport the aliens either into the past or the future. Must have been invented by Doc Brown.
Multi-Melta = Fusionskanone
This weapon would melt the feet of the aliens to the space hulk´s floor. Why they wouldn´t pose any danger anymore in such a state is to this day an unsolved enigma...
Conversion Beamer = Degressor
This weapon would alter the alien mind chemistry to become docile, harmless creatures. So instead of running amok they would leave the ship in order to spend their time plucking flowers on a grassy meadow.
Power Glove = Schockhandschuh
This weapon would incapacitate aliens in the same as a taser would. Hope the aliens have strong hearts or else this could prove fatal as well.
Power Sword = K.O.-Schwert
This weapon would knock out aliens like a punch from Mike Tyson. While not necessarily deadly such treatment can still cause concussions and various other ill brain defects later on.
Bolter = Laser
Strangely there wasn´t any satisfying explanation for this weapon provided in the rules.
Apart from being a nostalgic voyage to days gone by I intend to use his thread to come up with more unique ideas for non-lethal effects for ANY kind of
40K weapon which hasn´t been covered by the rules from the 90s. The weapons themselves doesn´t need to be of Imperial origin. So lets be creative:
Power Fist = Bro Faust
Yes, I know the power glove/fist is essentially the same weapon but the opportunity to describe the following weapon effect is simply too good to be ignored.
This weapon would force the alien to greet the attacker via a "bro fist" gesture thus befriending them in the process. According to the
40K lore Blood Angels (=
GSG Tiger;
LOL!) were very fond to use this weapon against Necrons (=Androids).