bbs100 is a BBS in the style of DOC and/or YAWC. DOC is a style that remotely resembles Citadel. What's special about bbs100, is that it's a single process daemon that handles all connections at once, while consuming very low cpu resources ( < 1%). It can handle over a thousand simultaneous users. It is highly customizable, is easy to setup, and has many configurable features. bbs100 is almost a must-have for people that want to run a DOC-style BBS.
Citadel is an advanced messaging and collaboration system for groupware and BBS applications. Users can connect to Citadel using any telnet, WWW, or client software. Among the features supported are public and private message bases (rooms), electronic mail, real-time chat, paging, shared calendaring, address books, mailing lists, and more. Unlike other collaboration servers, Citadel provides its own data stores and is therefore extremely easy to install; you don't have to "bring your own" email and database because they're built in. The server is multithreaded and scalable. In addition, SMTP, IMAP, and POP3 servers are built-in for easy connection to Internet mail. Citadel is both robust and mature; it has been in production since 1987.
Pipo-BBS allows you to install a BBS server and clients. You can chat via a nice interface with an unlimited number of people (as with IRC). This software is in a pre-release state; it is still very alpha, and can be difficult to even compile. It works under linux, MkLinux, SGI, HP-UX, and Solaris. The only interface for this BBS is telnet for the moment; an interface using GTK has been started. It has been translated into French, English, Spanish and German.
Ncohafmuta is a text-based chat server that is designed for access from a telnet client. Its purpose is to allow users to communicate in a configurable environment in realtime. It allows users to create accounts with their own settings and optional personal information. Rooms are the basis for communication, whether private or public. Other features include internal email, email forwarding, a configure script for multiple Unices, support for cygwin under Win32, macros, games, a ranking system with access to more commands, ANSI coloring, banning, async DNS, soft/hot-rebooting, detailed, organized logging, and an internal Web server port.
Amethyst started as a port of Infobot to POE, continuing as a generic bot core with the ability to handle multiple connections using different protocols (not necessarily IRC) and soft route the incoming messages through a number of processing centres. One of these processing centres contains much of the original Infobot core.
Volley is a modular client/server application for chat, file sharing, and so forth. It is similar to Hotline, except its modular design allows for the addition of more services than just the usual chat, files, and news; there could be multiplayer games, and online meeting tools such as virtual whiteboards.