The project consists of a backplane with an SPI bus that has 8 slots for IO cards that use the industrial standard 24VDC levels.
The outputs can directly drive valves, contactors, and other actuators to control equipment. There are sinking and sourcing output cards and an isolated input card that can be strapped as either sinking or sourcing. I will assemble the necessary drivers and release a demo PLC program in C with ncurses under the GPL. The Hardware PCB, Gerber, BOM, Schematic, etc., files will be released under an Open license, probably Creative Commons. Anyone will be able to reproduce the project under that license.