Operating system of IBM AS/400 mainframes. Transaction-oriented; nothing to do with AIX.

Tcl/Tk has been ported there: [http://www.export-ventures.com/tcltk.htm]
   * Tcl 7.6, Tk 4.2
   * Requires OS/400 V4R4 or later
   * The distribution includes the XLIB portion of X Window/400, the Tcl command interpreter, and the Tk (wish) console  OS/400 V4R5 is required DB2 access.
   * [VTCL] - a GUI builder written completely in Tcl/Tk by Stewart Allen, is included free of charge.
   * REXEC and RSH (Remote Shell) - two remote execution command daemons for starting AS/400 applications and commands from remote workstations.
   * 15-day free trial download, after that it costs about USD 750.