[Explain. Analyze.]
http://x3270.bgp.nu/tcl3270-man.html
http://packages.debian.org/oldstable/net/tcl3270
http://www.geocities.com/SiliconValley/Peaks/7814/
http://freshmeat.net/projects/x3270/
This appears to be an application which can talk (via IBM's 3250 terminal protocal) to IBM mainframes.