Obsidian is an extensible virtual world system with a fullblown multiplayer client-server architecture. It is not a VRML2 world system, though there are plans to include VRML2 as a world data format. Note that active development on this system stopped a while ago, though the code is still available for the curious. The code may not even compile on current Linux or Irix systems.
RoboCommish is a Perl-based Fantasy Football League(s) Management suite. Features include automatic weekly game downloads and statistic processing; independent multi-league scoring; report generation (text and HTML) and extreme customizability. The Perl implementation is intended to be OS agnostic -- both Unix/Linux and Windows distributions are available.
Xws is a text mode multi-player crossword and chat server. It presents the same puzzle to everyone, allowing people the option to try and/or discuss solutions. Play may be friendly collaboration or fierce competition, depending on the players' dispositions. Xws supports hundreds of puzzles in the popular Across Lite file format. Copyright issues prevent the distribution from including any puzzles, but several archives and resources are listed in the README.
ymusk stands for Yenzie's Mush Klient. It is a mush client written in Perl, and it is built around the Net::Telnet and Tk modules. It is meant to be a simple program which is easily customizable. Its features include logging, macro definition, speech filters, command history, and ANSI colors.