LinuxDoc is an SGML DTD which is similar to DocBook. Matt Welsh created it, and version 1.1 was announced [1] in 1994. It is primarily used by the Linux Documentation Project. The DocBook SGML tags are often longer than the equivalent LinuxDoc tags.[2]
LinuxDoc has a more succinct DTD than DocBook. Users of small to medium-size projects have found that it suits their purposes better than DocBook.[3]
The Debian distribution of Linux has a Linuxdoc-tools package.