GOVERNMENT: US Department of Defense

According to this report, Tcl/Tk and Expect are used at the US DOD:

although they don't go into the specifics.

Tcl 8.3 is blessed by DII COE [1 ] as a COE Product. This effectively means that you can acquire this software directly from DISA. Perl is the only other scripting language listed (as of COE Version 4.6 Build List for Solaris/Windows/HPUX 09Jan03).