Bootloader developers used to be particularly fond of Forth.

For example, for many years the FreeBSD's 3rd-stage loader used FICL (Forth Inspired Command Language) for scripting [1]. It's still supported, although in the recent years it was deprecated in favor of Lua [2].

[1] https://github.com/freebsd/freebsd-src/tree/main/stand/forth

[2] https://github.com/freebsd/freebsd-src/tree/main/stand/lua