Open-source boards designed in KiCad by bitomaxsp on GitHub, from 3 repositories. A board’s address here is its repository’s there.
bitomaxsp/rca-wv98c
RCA WV98C schematic and PCB in KiCAD
bitomaxsp/rs-ttl
RS232 to TTL converter
bitomaxsp/UNOvx
Arduino-like ATMega328 board