[aidenn0]

I'm blanking on the name, but there was an older 5-way switch keyboard, where the 4 non-thumb fingers went in a recess with 4 paddles and a push-button; I've known several people who used that because of severe RSI, but it was quite expensive.

[edit]

Searching split keyboards on google image search for long enough found it: https://en.wikipedia.org/wiki/DataHand#/media/File:DataHand_...

[nomel]

Yes, this is actually what lead me to the CharaChorder! The data hand seems superior for single letter entry, but the CharaChorder has a type of chording built in to the firmware. I imagine sticking their chording engine in the DataHand would be incredible.

[0xdada]

jesusfreke has a 3d printed version of this on github: https://github.com/JesusFreke/lalboard