IRISconsole Silicon Graphics ships IRIX 6.2 with sgitcl , a very, very cool installation of tons of Tcl tools and applications. SCO does the same. Midnight Networks, Inc. offers a remote-access tester of PPP, IP, and modems. Tcl is its extension language. It's a BellCore system which relies on Tcl.
Myriad is an integrated system for combinatorial chemistry informatics.
National Semiconductor has constructed an Electronic Design Automation Environment. They keep it in-house, to the best of my knowledge. Cray's Network Queuing Environment uses Tcl as an extension language. NExS is a Unix-hosted spreadsheet with connections to Tcl. Dirk Vermeersch's Object Domain was marvelous as shareware, and now it's a very competitive commercial OO CASE tool which supports Booch and OMT notations.