Xinu - "Xinu Is Not Unix". A Unix-like operating system. Originally developed in the 1980's.
Apparently xinu uses Tcl.. From the documentation:
"The Xinu shell also understands Tcl scripts. A few sample Tcl scripts have been included and are described in the TCL(1) manual page."
According to the xinu page on wikipedia [L1 ].. it 'continues to be used for operating systm and networking courses at universities around the world.'
I stumbled upon it when looking around at stuff related to z80 based embedded processors.. it seems Zilogs 'eZ80' processor 'supports a free TCP/IP stack and operating system based on XINU'. I wonder if this also runs Tcl - and what versions?