TV OSW [L1 ] is I think a University of Berkeley project to make musical instruments with blocks, which uses Tcl/Tk as part of the user interface.
It uses a multi-threaded version of Tcl (See Tcl and threads thread I recall compiling 8.6 on Fedora and probably having the option --enable-threads , check by: puts $tcl_platform(threaded) ) and Itcl.
(screendump of opening screen:)