At the company I once worked for I used a NeXTcube to demo a co-processor board built from VHSIC Phase II chips. The cube's size and form factor allowed for a nice sized board to be plugged into the backplane. And the graphics of the NeXT were pretty advanced for the time. The co-processor board ran a missile tracking algorithm on canned data and the NeXT painted a nice real-time graphic of the tracking. It made for a really cool demo.

Steve Jobs actually paid a visit. When he saw the demo he said "That isn't what we had in mind." We thought he was kind of thick, that he didn't get it that when you have a cool product then users are gonna user and figure out all kinds of different things to do with it. Later it became clear that he was all about controlling the user experience, so seeing what we did was very contrary to his way of thinking.