The PlayStation Classic relies on the open source PS1 emulator PCSX ReARMed to play i

• Classic and mini versions of retro game systems have become popular to release onto the market, including the recently announced PlayStation Classic. With a very basic UI, and the chosen lineup of 20 games, many fans were disappointed and claimed that Sony's attempt at a plug and play throwback console was low effort. Complaints only furthered when it was revealed that Sony wasn't creating or reusing their own PlayStation 1 emulator for the Classic, like they had done with the PSP's POPS emulator, or with the PSP emulator that was found within the PlayStation 4 remaster of Parappa, or the emulated PlayStation 2 classic titles on the PlayStation 4 as well. Instead, Sony has opted use an emulator made by the public: PCSX ReARMed. At an event showing off the upcoming hardware, previewers were able to try out the PlayStation Classic, and found a menu listing stating that it uses open-source software, including PCSX ReARMed.
  
  via https://gbatemp.net/threads/the-play...-games.522857/