Xmess is the unix port of the multi emulator super system. it is similar in spirit to xmame, with the difference being that xmess emulates consoles and computers instead of arcade machines.
you need the roms of the system you want as well as software.
this package provides support files such as crcs for software, more information for the systems emulated and more. to get the actual emulator, install the xmess-x package.