NES 'Mission Control' Development system created by Rocket Science Production to test game development on the Nintendo Entertainment System. It seems Nintendo didn't have an official Development System in the early days of the NES, so some companies opted to build their own. Bill & Ted's Excellent Adventure and The Mutant Virus were developed on this system.

The system was connected directly to a modified NES via this cable (attached to the blue connector on the DevKit itself). Special RAM cartridges were created to load the game code into.

Here's the underside of the DevKit board displaying the insane amount of by-hand wiring that went into this...

These are the two cartridges that came with the system. The first one appears to be a 32K RAM cartridge for playing software on the system, the second one has a section cut out of it so you can attach a logic probe or scope to the cartridge to get an idea what's going on inside it...

Inside the cart labelled '32K'

Inside the other one with the logic probe connections.
There's at least two pieces of software that work with this system: NESTEST.EXE which was used to actually test/debug the debugging hardware itself, and HST.EXE which is the Mission Control software that actually communicates with the hardware.

Here's some screen shots of these two programs in action (these were run without the hardware attached to the computer, I have not actually attempted to power up the hardware yet...)

HST Control software brings you into a shell program (ROCKET is the prompt).
About 10 lines down I entered a '?' to get the help list of commands.

The menu screen for the NESTEST application.