I've read many times in the past that a lot of EDA-related software is written in Tcl and Tk.

Electronic Design Automation.

https://en.m.wikipedia.org/wiki/Electronic_design_automation

See:

https://www.tcl-lang.org/about/uses.html

The section about Embedded Development.

CAD is mentioned there too.

https://en.m.wikipedia.org/wiki/Computer-aided_design

Pasting that section's content here:

Because Tcl is a very compact language, and is easily integrated with special hardware, it is a popular choice for embedded development. You'll find Tcl hidden away on many devices, including many networking products from Cisco and others, and set-top boxes including Tivo. Embedding Tcl within other software projects is of course also hugely popular, and has become the dominant control language in some industries, such as in electronic design automation (EDA) and computer-aided design (CAD) applications.

More generally:

https://www.tcl-lang.org/about/uses.html