Mednafen is a multi-system emulator, driven from the command-line.

Mednafen is a multi-system emulator, driven from the command-line.

Many of its cores are ports of other emulators, but many of them are also original.

Its Playstation and PC Engine original cores are notable for their high quality, compatibility and accuracy.

Mednafen only has a command line interface, so its interface might be hard to use to new users.

The best cores in Mednafen are those that are original - which are the PS1, PCE, PC-FX and Virtual Boy cores.

The PCE core is one of the best emulators for that system, with a Fast and Accurate version.

The PS1 core is native resolution only, and features high degree of accuracy and compatibility.

The Virtual Boy core is one of the best for the system, although it does not attempt to reproduce the 3D.

Other cores improve upon emulators that have been long abandoned and rarely updated. These include the Neo Geo Pocket, WonderSwan Color and Atari Lynx cores.

Other cores are less useful, as there are better options in stand-alone emulators (NES, Genesis, Master System and SNES). These cores might even be based on out-dated versions.

For instance, the SNES core is based on an old outdated version of bSNES. This is before the performance/accuracy/balanced cores - 0.50x territory - with a couple of changes by Ryphecha.
Core Features.

Physical joystick/gamepad support.
Versatile input configuration system; assign multiple physical buttons to a virtual button or action.
Multiple graphics filters and scaling modes.
Save states.
Real-time game rewinding.
Screen snapshots, saved in PNG format.
QuickTime movie recording.
MS WAV-format sound logging.
Loading games from gzip and (pk)zip compressed archives.
Network play(utilizing an external dedicated server program).

To play a game that consists of more than one CD, and you are using ripped disc images, you will need to create an M3U file(plain-text, ".m3u" extension), and enter the filenames of the CUE/TOC/CCD files, one per line. Load the M3U file with Mednafen instead of the CUE/TOC/CCD files, and use the F6 and F8 keys to switch among the various discs available.

Note: Preferably, your M3U file(s) should reference CUE/TOC/CCD files that are in the same directory as the M3U file, otherwise you will likely need to alter the filesys.untrusted_fip_check setting.
Support for multi-disc games when using physical CDs is somewhat clunky. To begin with, you'll need to start Mednafen with the first disc of the set in the drive. To switch to a different disc, press the F8 key, which should eject the disc. If the disc fails to eject, use the drive's eject button, and press F8 again so that Mednafen displays a message like "Virtual CD Drive Tray Open". Place the disc you're switching to in the drive, close the lid/tray/whatever(if applicable), and press the F8 key again. If you're using a standard PC-type drive with extending tray, you may just press F8 to close the tray instead of manually closing it and then pressing F8.

Screenshots.