It's a 3D printable screwdriver handle for 1/4" hex bits.
NEW! - Now with a compartment to store 7 bits
Inspired by tomlambardi's thing I made one slightly bigger and with, hopefully, a better grip.
I struggled to push my bits into the original so I made the hex flats 6.5mm rather than 6.35mm (1/4") If it's still too small try pushing the bit in just as it finishes printing, while it's still warm.
Just print it with fill on. Denser fill will probably make it last longer.
I'm thinking of opening up the insides and adding a screwcap to the bottom so you can keep a few bits inside...
Update - I've added a slighter bigger version which has a screwcap lid and cavity to store bits. I'd recommend 0.2mm slice height or less, to get a decent working thread. You'll need support on the main screwdriver but I found the lid builds OK without it.
Thanks for everyone's comments so far - I have to say it's probably the most useful thing I've ever printed :)