One of these: http://www.computinghistory.org.uk/det/33101/Acorn-Cambridge... with a TI 32016 processor & using a BBC Micro for UI - except that my housemate Colin thought it was a bit expensive, so reverse engineered the board, redesigned it to be a little smaller (this was in the mid-80s & chip specs were changing rapidly), wire-wrapped a prototype for testing, then etched five proper PCBs, of which only a couple were populated.