What's an easy way to connect multiple pins between multiple breakout boards?
Add in even more breakout boards to serve as connective splitting junctions.

If you are using female crimp housings at the ends of your wire then solder rows of headers onto little protoboards with a strip pattern. The strip patterns are probably longer than you need so use a knife to cut them up into smaller segments.


Busboard

If using male headers or solid-stranded hookup wire, then you can just buy small miniature solderless breadboards.

Solarbotics