I'm looking for unusual and/or surprising examples for interpreters or JIT compilers in places one would not necessary expect them to be used in an operating system at runtime (in the widest possible context). The idea is to discuss and explore hidden overheads in system software with my students in the context of a seminar and/or project.

Obvious IMHO not-so-surprising examples are shells or (e)BPF/Dtrace scripts.

Some more unexpected uses I can think of are interpreters for vector fonts (e.g. PS Type1 or TT hints), the use of LLVM to compile shaders for CPUs [1] or the use of Prolog in the network configuration of NT4 [2].

Do you know other examples?

[1] https://llvm.org/devmtg/2007-05/10-Lattner-OpenGL.pdf

[2] https://web.archive.org/web/20040603192757/research.microsoft.com/research/dtg/davidhov/pap.htm