SOG Double Key, that has locking knife and fingernail file blades, to go on an EDC keyring. I'd purchased the SOG Key Knife, shown for size comparison, a couple of years ago, and it's been off and on my keyring a few times as I rotate various gadgets that I EDC.
The locks on the Double Key are pretty close together, so it can be a bit awkward unlocking them when you want to close whichever you're done using, but they otherwise function alright. The tool is a bit thicker/heavier compared to the older version, and both are larger than house keys, but I still find them okay for key chain carry.
I find the Leatherman Squirt P4 preferable as my 'go
to' EDC tool on my key chain, but I think the Key Knife and Double Key
can make useful gifts for friends and family that aren't particularly