Tcl
Beginner
A simple language for typing commands. Most chip design programs understand it, so engineers can save their steps instead of clicking.
Novice
Tool Command Language, a small scripting language that programs can build in. Most chip design tools, open and commercial, take their commands in Tcl, so an engineer can save a sequence of commands as a script and rerun it exactly. Timing goals (SDC files) are written in Tcl syntax too.
Expert
Written by John Ousterhout, who also wrote the Magic layout editor. Its small interpreter is easy to embed in a C or C++ program, which made it the usual command language of EDA tools. Newer tools add Python on the same internal data, but most flow scripts and every SDC file are still Tcl.
Explained in Tool landscape (Extras).