The Balthazar Personal Computing Device (BPCD) is an open-source hardware 13.3-inch laptop with a RISC-V, Arm, or FPGA module and designed to be upgradable, expandable, and sustainable.
The developers say the laptop is based on a few concepts inspired by the EOMA68 project. The EOMA68 is a CPU module based on the PCMCIA form factor, and an Allwinner A20 EOMA68 module was showcased in a prototype of the Rhombus Tech 15.6-inch Libre Laptop but I don’t think the project was ever manufactured.