Xmame is the X11 port of the MAME arcade game emulator.

MAME is a virtual machine emulator; it includes emulators for the CPUs,
sound and video chips used in game consoles, as well as special purpose
PALs and detailed information about the memory layout of each machine.

MAME is a virtual machine emulator; it includes emulators for numerous
CPUs, sound and video chips used in arcade games, as well as special
purpose decoding PALs and detailed information about the memory layout of
each game.

MAME now also includes MESS, an emulator for various game consoles.

To play games in Xmame you must have a copy of the original game ROMs.