Okay, I Like WezTerm

Oh, very cool that it uses Lua for its configuration. That opens up a massive potential for new behaviours and customization.

Emacs uses Lisp in a similar way. What other applications use a programming language for their configuration?

Not sure if it counts but the suckless project (e.g. st or dwm) use C (its source code) as config :)

Neovim is the obvious example here, also relying on Lua.

Neovim of course also supports Vimscript, although writing anything more complex is much nicer in Lua.

NeoVim also uses Lua and I think nginx does too.

awesome-wm!

probably the most popular instances of this approach are firefox, chromium, and safari. the unix shell, godot, unity, unreal engine, truetype, and postscript are probably also worth a mention

XMonad (a window manager) uses Haskell.