https://www.retrorgb.com/rip-universal-game-cases.html
There are other cases, such as Custom Game Cases and BitBox, but UGC had two main benefits over them. One, UGC fit a variety of game carts. So say I need 75 for SNES carts and 25 for N64 carts, I could purchase 100 UGC and be good. But with the two above mentioned alternatives, the cases are specific to a specific cart. So if I purchase 100 SNES cases to get that price break discount, if I have 25 left over I wont be able to do anything with them. And two, UGC was the cheaper option. Even with quantity discounts, the two mentioned alternatives are much more expensive. Also, the BitBoxes require a strap to hold in an instruction manual which is an additional cost. It looks like without the strap it would be annoying to close the case with a manual (and possibly damaging the manual).