During Toaplan's tumultuous Toaplan 2 hardware era (1991-1994), two of their arcade games went to waste. The first one is Dynamic Trial 7, which was a linkable multiplayer racing game; despite having all the advertising, it got a lukewarm reception at the location test and was shelved. The other is Genkai ChÅsen Distopia, a side-scrolling action game full of monsters; it was doomed by Toaplan's bankruptcy, and none of the splinter companies (Cave, Gazelle, Eighting, Takumi, etc.) picked it up.
While PCBs of both are known to exist, the two currently-known PCBs of either are in sticky situations. Finding an unreleased/prototype arcade PCB is harder than finding such a console or computer game, but from what I can tell, D-T 7's board number is TP-029 while Distopia's may be TP-028 in case you want to hunt these things yourself. If you are an active MAME contributor, I wish you the best of luck in hitting this jackpot.
I got into contact with the director of the upcoming documentary All Your Base Are Belong To Toaplan, and he stated that he doesn't know who composed the music to Distopia. I predicted Toshiaki Tomizawa (FixEight and the absolutely delicious Vimana), but he had no involvement in the project, with the director predicting that Tomizawa could've instead scored D-T 7. He too wants to know more about the games, so at least I'm not alone.