I’ll go first.
When I was a kid my family had a TI-99/4A. The 99 series was Texas Instruments’ only real foray into the PC and video game market, and it failed to be competitive with Commodore, Atari, and Amiga. Most games were booted from cartridges.
My favorites were Hunt the Wumpus, a sort of early survival-horror with a turn-based grid system, and Alpiner, a mountain-climbing game with various hazards, kind of a reverse SkiFree. It also had the ability to read data from cassette tapes to load text-based games. The one I remember is Hammurabi, a sim/strategy game which I didn’t really get as a kid. Now that I’ve gotten into strategy games like Civilization and Romance of the Three Kingdoms it would be interesting to revisit.
My neighbour had Sega Channel when I was a kid. So ahead of its time. I know it’s not a system, but it was certainly obscure. I’ve never talked to anyone who knew what it was.
Sega was just ahead of its time for so long.