The PS4 is nothing if not a versatile machine. Able to play some of the hottest games on the market today, it's no wonder its sales have reached record numbers.
That said, the PS4 is not without its fair share of problems. One of the biggest right from the start has been lack of backwards compatibility. The PS4 is not backwards compatible with PS3 games, nor with PS2 or PS1 games for that matter. It's a sticking point for a lot of people.
While emulators do exist for each previous PlayStation on PC, it's not quite the same as hooking up to the real deal. That particular itch has been scratched for one PlayStation console, however, namely the PS1. An enterprising hacker found a way to emulate PS1 games on the PS4, all thanks to 2019's MediEvil remake. MediEvil 2019 has the entire PS1 version of the game contained within on an emulator program, and it turns out that, with a little tinkering, it can be used to play other PS1 games too.
The lack of backwards compatibility has been a big PS4 problem from the start and a sore point for some players, but many players still have physical copies of their favorite games handy. There's an undeniable sting that accompanies paying again to play a game already owned, so while it may not help with the previous generation of PS3 games, the PS1 emulator is a nice start anyway.
There is already a list of games compatible with the emulator, which can be found here. It is sparse in its current state, and many games have been found to be unplayable. That said, there is still room for experimentation before the PS5 launches. It's been said that the PS5 will have backwards compatibility anyway, though how far it extends is unconfirmed and likely to be limited to PS4 games. It's fortunate that MediEvil 2019 had the entire original game to unlock, and that people did so, or the emulator may never have been found.