blinkperl is a telnet server (written in Perl) which plays a random (ASCII-Art) Blinkenlights-Movie if a telnet client connects. In a properly configured system, you do not need a 'usual' telnet server (because of the plaintext password transmission, ssh is better and uses another port), so why not play ASCII-Art Movies on the telnet port?
DataReel is a free, cross-platform database and communications toolkit. It can be used to rapidly develop and deploy multi-threaded database and communications applications. The DataReel toolkit is composed of a modular C++ library designed to build cross-platform infrastructures for end-user applications, embedded systems, and reusable libraries. DataReel's unique modular design simplifies adaptation, allowing you to determine the level of complexity. DataReel makes Internet connectivity and database programming easy.
ZOC is a popular terminal emulator and telnet client that supports telnet, modem, SSH 1 and 2, ISDN, serial, TAPI, Rlogin and other means of communication. Its terminal emulator supports Xterm emulation with full colors, meta-keys, mouse support, and local printing; VT102, VT220, and several types of ANSI; and Wyse, TVI, TN3270, and Sun's CDE. Unique features include full keyboard remapping, REXX scripting, and support for connecting to named pipes.
vmodemd is a telnet server designed to run old DOS BBS systems and door games. It listens for incoming TCP connections on a defined port, does a minimal telnet handshake if needed, and then starts to proxy all data to a PTY which is bound to a dosemu virtual serial port. vmodemd supports any number of virtual modems, can display customized banners if all modems are busy, can terminate a serial app when a telnet connection is unexpectedly dropped, and run custom scripts before passing control to dosemu, allowing you to pass relevant data like incoming IP address to the DOS app.
This is the old BSD tn3270 made to compile under Linux/GLIBC. It is not perfect and not being actively maintained. Also in the same directory is 3270v4.1 from CERN, made to compile under Linux/GLIBC, which looks nicer. If you are interested in these programs, you may also want to look at the Linux tn5250 project.
PowerTerm InterConnect is a fast and secure terminal emulator, providing comprehensive emulation support via various communication modes. It meets the host access needs of many organizations, supporting the broadest and widest range of hosts, including IBM Mainframe, IBM AS/400, UNIX, OpenVMS, SCO, Tandem, HP, ANSI, Data General, Wyse, Televideo, and more. PowerTerm InterConnect offers state-of-the-art features, including SSH and SSL security, customizable function keys, multiple concurrent sessions, scripting, a menu bar, scalable and selectable fonts, intelligent copy and paste, printing, and more.