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?
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.
ansistego provides terminal-level steganography for scripts and other ASCII files (ie, protection against 'cat'). It intersperses a text/script with commented ANSI codes that cause most terminals to clear sensitive lines as soon as they are written. Only a specified front text appears. The front text is embedded in the script using ANSI-cloaked comments, so that the text appears unaltered when the script is viewed with cat, but the script can be run without any decoding stage.
gtermix is a GTK+ telnet client intended for calling BBSes. It utilizes a custom VGA textmode emulating terminal widget that allows it to accurately render bulletin board systems as they were in DOS terminal programs. It currently features a GTK+ user interface, dialing directory, support for ANSI, vt100, Avatar, and TextFX terminal emulations, and proper rendering for DOS-style BBSes.