Two-ball trackballAn open-source, fully programmable two-ball, three-button USB trackball by jfedor2.
Not a keyboard, but another nice companion.
The GitHub repository linked below contains design files and code that can be used to make a fully programmable two-ball, three-button USB trackball:
Published on Mon 22nd Nov 2021. Featured in KBD #53 (source).
The cocot46 is a homebrew keyboard with an integrated trackball and rotary encoder.