These can be either games you designed, you played as a playtester, or you saw prototypes of that you liked but they never saw the light of day. I'm curious to know your favorites.
About 10 years ago I made a prototype of All Your Mech (the name was a play on the All Your Base meme, and was just a placeholder). It was a simplified role-playing boardgame, sort of like Battletech, but designed to play either as one-off scenarios like a typical boardgame, or prolonged campaigns more like an RPG. The big feature was designing your mech, using transparencies to overlap each other to form a full mech. That way, you could swap out individual transparencies to customize or improve your mech. Reference the image below of the transparencies stacked together on top of the mech character sheet to see what I'm referring to.
Every playtesting session was a lot of fun. So why didn't it take off and instead got shelved? The cost of making the transparencies. Even overseas manufacture would have forced the game to have a $125 retail cost to make even a tiny profit. And 10 years ago that just wasn't feasible compared to what content you were getting in other boardgames you see at the store. I'd have to sell 25,000 just to make it worth it.
Maybe one day...
(https://scontent.fhio2-1.fna.fbcdn.net/v/t39.30808-6/466621086_10235233697926443_7433501332455611452_n.jpg?_nc_cat=111&ccb=1-7&_nc_sid=aa7b47&_nc_ohc=VQkzBipkW5IQ7kNvgH4ouiK&_nc_zt=23&_nc_ht=scontent.fhio2-1.fna&_nc_gid=AV7olhmirb868cN2tJH9Y_Y&oh=00_AYAd5CnbGKNehGmc0IDYIAPQMVesasogyqKHRA86BRssSw&oe=673AAD1B)
(https://scontent.fhio2-1.fna.fbcdn.net/v/t39.30808-6/466840609_10235233697886442_4037334491125038140_n.jpg?_nc_cat=103&ccb=1-7&_nc_sid=aa7b47&_nc_ohc=_--_Qn54-uIQ7kNvgHkCw8l&_nc_zt=23&_nc_ht=scontent.fhio2-1.fna&_nc_gid=A4W_n7wBPOcof0W4-ecHibC&oh=00_AYDpLs3yMGxtn3GEGgh83tltAjM0E9j0mE7LJRDRI6nTOA&oe=673A962D)
(https://scontent.fhio2-2.fna.fbcdn.net/v/t39.30808-6/466684273_10235233697846441_4166099278782411934_n.jpg?_nc_cat=110&ccb=1-7&_nc_sid=aa7b47&_nc_ohc=BQSyHwj4MIkQ7kNvgE2ZP-X&_nc_zt=23&_nc_ht=scontent.fhio2-2.fna&_nc_gid=AeUJ-7Eol86748w-dXHdhEl&oh=00_AYCnIng19emxRBLQOvj6WQD250QFICpJWF9RrKlRfM8Bqg&oe=673AA924)
Wow. That's a very, creative idea using the transparencies. It allows versatility in swapping out different parts, and it also gives the player a nice visual of the completed mech.