Built in KiCad and fully autorouted with Freerouting.
Same size as a Pro Micro (18x33mm), has both MicroUSB and Type-C, Li-Po charger and BT 5.0.
Runs full-featured QMK software (nrf52 fork), uses USB Mass Storage for firmware updates.
Runs fully wireless split keyboards over Bluetooth, does NOT need TRRS cables or receivers.
Supports wired split keyboards via USB-C, MicroUSB and I2C/Serial extension cables.
The nrfmicro project is well documented, you can find all the necessary info to build and use one at: https://github.com/joric/nrfmicro