Tool balancer is the name you seek..
You want to make sure the one you pick is adjustable for the weight of the tool, some are and some are not.
Plenty to choose from
HERE starting as low as $20
My now former employer threw out at least 40-50 of them a long with many tools, benches and inventory after they were bought out and competing product production lines were stomped out.. Never thought to grab a few, I have a pretty darn heavy spot welder that is next to impossible to keep lifted..