Superguy is the other shared universe superhero writing group from before the dawn of the Internet, the DC to the LNH's Marvel (unless it's the other way around). It predates the LNH by about three years. Where the LNH originated on Usenet, Superguy originated on the academic network BITNET, though it currently inhabits a mailing list.
While both Superguy and the LNH revolve around superhero parody, there are considerable differences: Superguy focuses on more general superhero parody rather than specific comics parody; it lacks the LNH's basis in computer terminology and Usenet; it has more satirical use of real-world figures; and it often directly lifts concepts from other media, fanfiction-style, rather than creating trademark-friendly parodies.
In 1996, Dave Van Domelen's LNH series Dvandom Force and Chris Meadows's Superguy series Team M.E.C.H.A. crossed over in a storyline known as the Grand Tour, together with several other writing groups Meadows was involved in. The storyline revolved around DeFacto V recruiting minions from both the Looniverse and 000SUPERGUY in order to return to his original timeline. Many elements from RoboMACs 2163 stuck around as long-term parts of Team M.E.C.H.A. after this crossover.
Mike Escutia also wrote a brief LNH/Superguy crossover, Auld Acquaintances, and after finding that he preferred writing in that universe, moved several of his characters over to that world in Stolen Hearts.
Birth of a Villain introduced a net.villainess called Vector, who was also the name of an villain from Dave Van Domelen's Superguy series, Crazy Guy. He wrote a brief cameo from that series' heroes, Jack and his squirrel sidekick Louie, to comment on this, but other writers picked up on them. They were later explained as Jack and Louie's LNH counterparts, Chinese Guy (AKA Bruce) and Lenny the Squirrel. Later, counterparts of four Dvandom Force members were brought to the Superguy multiverse in Exarchs and its sequel New Exarchs.
Unfortunately, Superguy has not been as successful in keeping up activity as LNH, and the flow of stories has slowed to a trickle. Still, both new posts and the archives can be read via the Superguy Autocollector, at http://archives.eyrie.org/cgi-bin/superguy. The FAQ is available at http://archives.eyrie.org/superguy/TEB/Frequently-Asked-Questions.gz. And to sign up for the list, or just to learn more, check out the Superguy Info Page.