A rather simple screwdriver handle modeled after very comfortable Krafool ones. I personally like this design more than any other i've used, and decided to make a bunch of these.
Designed to have a standard magnetic bit holder inserted and wrapped with some grippy material, textile-based rubberized electrical tape for automotive wiring works great.
Do remember that this is not meant for very heavy duty and high torque!

Files included:
Loose fit - hex slot has 6.7mm space, the bit holder can be inserted with light force, you will need to apply superglue or epoxy to fix it in place
Tight fit - hex slot has 6.5mm space, the holder will probably need to be pressed in with a clamp or vise. Brittle plastics like PLA or ABS might crack, PETG works fine
Ribbed versions - handle has 3 ribs for some added grippyness, though i like the normal version more
*If your printer tends to mess up the object dimensions you might want to do a test print and tweak the model scale

Printing: print vertically with the slot facing down, if you have poor bed adhesion - add an outer brim. 15-20% infill of your liking (i use gyroid), 3 or more perimeters. Use any hard material, PETG works nicely. For added strength you may use a modifier to have higher % infill around the hex slot.