Hey... isn't that just a photo of a cable? Yup. To be precise, it is what is sometimes called a LapLink cable (except in that we happen to have wired it with extra grounds for better noise immunity). We call it CAPERS: the Cable Adapter for Parallel Execution and Rapid Synchronization.
While we were busy improving the TTL_PAPERS library, we realized that it would be possible to implement a version for two processors using only a passive parallel cable connection between the machines. This doesn't scale, but it sure makes it easy and cheap to try out the library. Aside from the inability to scale, performance is slightly worse than using the TTL_PAPERS hardware.
The only thing set in stone is our name.