He might want to know that it's a bit tough to properly publish for the following systems without getting either 1) getting a license or 2) potentially infringing patents and/or copyrights (this is just FYI; I can't tell you for sure what is/isn't legal):
NES - uses a patented lockout scheme (though there's a good chance that the patent on this one expired). This can theoretically be worked around with an adapter, the lockout chip in the system can be disabled, and from what I've heard the top-loading NES systems don't have one to begin with.
Super NES - uses a patented lockout scheme similar to the NES one. This can also be worked around with an adapter or by disabling the lockout chip; import stores in some areas (used to?) sell the adapters because the lockout chips for PAL and NTSC systems are incompatible.
Sega CD - requires a Sega program to be present on the disc (you can't write your own replacement because it's compared byte-for-byte with a copy in the BIOS, specifically for the purpose of screwing over unlicensed publishers)
Saturn - same as SCD, plus the patented security ring scheme
Dreamcast - same as SCD
However, Sega doesn't seem to particularly care about these, if the DC homebrew scene and Good Deal Games (unless they're licensed, but if that was the case wouldn't they get to use the Sega CD logo instead of their slightly dodgy "For use with Sega CD systems" label?) are any indication; the Sega v. Accolade ruling also suggests that this might be considered fair use anyway. Still, he might want to get in touch with Sega, as they (well, Sega of Japan, anyway) don't seem to have that much of a problem with licensing stuff on their "dead" systems (stuff like Street Fighter Zero 3 and Vatlva were published on Saturn while the DC launch was in full swing, and it seems that there are still a few companies publishing Dreamcast games).
