Dunnet is a text adventure written by Ron Schnell in 1983. The game enjoys certain popularity because since 1992 it is part of the default packages in many of the Emacs versions. The word Dunnet is derived from the first three letters of dungeon and the last three letters of Arpanet. It was first written in Maclisp for the DECSYSTEM-20, then later re-written in Emacs Lisp so as to be more portable.
Dunnet is playable on any operating system with the Emacs editor. Emacs comes with most Unixes, including distributions of Linux and Mac OS X. It can be run by running emacs -batch -l dunnet in a shell or the key sequence M-x dunnet within Emacs, the former being the preferred and official way to run it.
Source: Wikipedia, "Dunnet (game)", available under the CC-BY-SA License.