Hidden Palace is known for sharing details on prototype builds of games and recently released a treasure trove of content. This time around there are nearly 180 prototype builds preserved and in the process of being documented.
Most interestingly is that thirty of the prototypes uncovered are for unreleased titles. This means games such as Bio Force Ape that were never released on cartridge. It also includes specific ports that never released, such as the version of Spot Goes to Hollywood for the Sega 32X. Other platform versions released back in the day but never the 32X one for whatever reason.
Folks interested to see the progression of their favorite games from prototype to production should definitely check out Hidden Palace.