Demonground can refer to either of two things in a /tg/ sense. The first is terminology from the horror game Dark Conspiracy, referring to areas where portals to nightmarish other realms have opened, allowing their denizens to infiltrate Earth. The second is a horror RPG netbook series.
The Demonground publication was a shortlived fanzine - originally for Dark Conspiracy, hence the name, but it branched out into other horror games of late 90s and the early 2000s. Created by a bunch of Dark Conspiracy fans who met in a chatroom, it ran from October 1998 to September 2002, but then sadly fell under whilst editing issues #16 and #17 - content planned for those issues did make it into Protodimensions before that publication met its own sad demise.
- http://42north.org/demonground/ - Demonground's website, with downloadable back-issues.