Typically DIY inter-board cabling is either insulation displacement (IDC), some sort of DB-9/15/25 or a variant of RJ-11/12/45. Heathkit used to have folks build cables with Molex KK crimp on connectors (which was very time consuming) but you could combine things like power lines (AWG22) and signal lines (AWG28) into the cable bundle. Today there is a tremendous number of connectors for which making your own cable is problematic at best, for example the .5mm spaced IDC cables, or the FFC connectors like the camera connector on the RasPi. I looked into getting an LVDS connector for LCDs (typical laptop screen) to something more DIY friendly, tooling was $2500, and cables would be $25 each, minimum 10) Did I want to invest nearly $3K to get one cable? No, but if enough people were interested it gets to be lower cost. Setting up that infrastructure as a service (making cables in small to medium quantity) would be, in my opinion, quite aweseome.
I missed that because all of my cabling needs are easily met by manual assembly: most custom cables I make are for CPC (Circular Plastic Connector) "Cannon" type connectors and the Series III contacts are still doable by hand (although machines do a much better job of crimping). 2mm pitch connectors are the limit of my ability.
My biggest problem is doing a good job in volume. Thankfully I've found a wire processor with very low setup fees.
