pSX (or psxfin) is a PlayStation emulator.
pSX is very outdated and compatibility with games isn't very good. The only things going for it are that it has low system requirements and the interface is very comfortable and easy to use. The source code was never released unfortunately, so it cannot be updated.
Also, as it only emulates a USA console ("SCEA" is shown on the PlayStation logo screen, regardless of which BIOS you use) it triggers copy-protection in some games, such as non-US versions of Crash Bandicoot 3: Warped where the Load/Save menu moves and selects options by itself