Trackgammon
Trackgammon is one of my very first games, even preceding Havannah. I didn't as yet have the later focus on perfect information games. I was considering a backgammon type game along a track consisting of a sine and its mirror image. For pieces I employed a set of the Towers of Hanoi with the usual restriction of placement. Since both players moved a set along the tracks in opposite directions, equal discs would capture by replacement, sending the captured disc to its starting point, where it would be inserted according to size. Imagine something like the two player board above. Players would meet only on the intersection points and thus be safe on the others. Rebuilding the stack at the other side of the track would be a 'last out first in' affair.
It took some experimenting, and my future ex provided the board, made from a piece of cloth with the tracks sewn into it.
The sudden realization that I could cut the track, bend it and insert a third or fourth leg, instantly turned it into a two-, three- or four player backgammon type game, on an 'each on his own' basis. That was great. My future ex set to sewing the other boards. That was quite a pack of cloth.

Much later I saw the dissection into board segments that would fit together to make boards for two, three or four. I had a nice set, but then I had a lot of nice things the day SE Fireworks exploded at 120 meters from my future ex house. I never offered it to any manufacturer, but I think it would make a nice product.