After the 0xCB Pluto sporting an Atmega32u4, Jakob and Conor announced the 0xCB Helios with an RP2040 chip. Pro Micro/Elite-C compatible, open source, and available at keeb.supply as well.
The Pluto is based on the AtMega, Helios is based on RP2040. With this new IC the controller gets cheaper, but is way more powerful feature and space wise. You can do a lot more stuff with displays for example – 0xCB-dev.
Specs
Pro Micro/Elite-C compatible footprint
26 GPIO pins
16MB (128Mbit) of flash
Dual ARM Cortex-M0 @133MHz
264kB SRAM
default off red power LED
blue user LED
a level-shifter to drive 5V components
onboard ESD protection chip
VBUS detection support for split keyboards
D+ and D- pads
"unbrickable" bootloader: its located in ROM on the rp2040 itself
single button reset circuit (reset the board with a short press and enter the bootloader with a long (>500ms) hold).
price: €17 (with headers for all three sides)
The one button reset circuit is based on the one used on the Sea-picro by Josh Johnson.
No silk art this time, the 0xCB team opted for a stealth design to go as sleek as possible so that the controller blends in with most keyboards.
Seeed Studio is running a sponsorship campaign of the Seeed Fusion Assembly service offering free PCB prototypes for DIY keyboard projects with a XIAO RP2040 controller included.