There are a large group of people working on emulation projects for various consoles and home computers. Emulation is a very grey area as regards the legality of machine emulation. The majority of manufacturers of old consoles and computers are happy to allow emulation although certain manufacturers such as sony specifically forbid it.
Emulators are usually either written for a specific machine or range of machines from a certain manufacturer or global emulators which cover a whole range of machines from different manufacturs.
The most popular global emulators are:-
M.A.M.E. – This is a global emulator for arcade game machines. The current version emulates over 10,000 different arcade games. Although mame itself is freely available the required games or roms must be sourced by yourself as the legal situation as regards possession of these roms is a very grey area. Mame can be downloaded from the official mame website. There are a number of “front ends” or derivative versions of mame such as mame32 and mame32fx. Original arcade games were discrete logic boards and as such are emulated in individual chips but later games used optical discs or hard drives to store game data. These are therefore stored in a compressed hard drive or chd. Some of these chd images can be over 20GB in size and so the current size of mame and all the current games is just short of 200GB. There are a number of places to obtain mame roms a search on google will give you a number of options.
M.E.S.S. – This is a global emulator for many home computers and is loosely based on mame and can be downloaded from the official mess website. Again although mess itself is freely available the required games or roms must be sourced by yourself as the legal situation as regards possession of these roms is a very grey area. With mess you will will need not only the games but also the roms from the various home computers. There are a number of places to obtain mess roms a search on google will give you a number of options.
The most popular emulators and systems are listed on the individual manufacturers pages