ePSXe is a PlayStation (PSX) Emulator for Windows, Linux, Mac OS X and even Android. It is one of the most popular emulators available for the PSX and one of the most successful at emulating the system. ePSXe is considered to be one of the very best PSX Emulators that you can find.
It has been one of the most successful PSX Emulators, successfully emulating various parts of the PSX with little to no issues, like many N64 emulators however, ePSXe uses a plugin to extend certain functionality, allowing 3rd party devs to improve the graphics, sound and various other features without needing to modify the core. Don’t worry though, PSX does include a few excellent defaults so you don’t have to go hunting for the right plugin.
Recent versions of ePSXe have moved to try and improve the accuracy of the emulator and introduce support for a HLE version of the bios, this means you wont have to go hunting for the PlayStation bios files anymore. While its still a work in progress, the OS HLE is showing that it can be done, although compatibility is not the same as the actual bios at the moment.