[bch]

Tcl is (last I knew) still remarkably big on “the edges” of networks: f5/a10 devices (iRules scripting[0]), used to be (is it still?) used for Cisco iOS scripting[1], was used as the glue language for Tealeaf session/network capture[2] (when it was deployed as on-premises installation ), and control language for Argonne National Lab cluster control[3]...

[0] https://devcentral.f5.com/s/articles/irules-concepts-tcl-the...

[1] https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ios_tcl/co...

[2] https://help.goacoustic.com/hc/en-us/articles/360043736414-P...

[3] https://www.mcs.anl.gov/~wozniak/papers/Swift_Tcl_2015.pdf

[blacksqr]

Also heavily used in banking and trading systems (Fidessa).

[blacksqr]

Also heavily used in software testing, including DejaGnu for Linux binutils.

[blacksqr]

Also heavily used in health care information management (Infor Cloverleaf).

[blacksqr]

Chip design, internet routing, compiler testing, finance, health care.

A legacy language that's only used anymore when basic infrastructure really, really has to work.