Here are the STLs for the one-handed reddit keyboard I posted on the /r/functionalprint subreddit (Link to the post).
I'm not going to write a detailed tutorial on how to put this together, since it is very simple.
You need the following components:
The wiring looks like this:
The code for the arduino can be found here.
Simply flash the Arduino, put the switches in the lid, solder the wires together and you're good to go.
The author marked this model as their own original creation. Imported from Thingiverse.