Otherwise, something special with POSIX shell is its large number of independent implementations, making it the ideal starting point for diverse double-compilation (https://arxiv.org/abs/1004.5534). The idea is to bootstrap a toolchain from multiple compilers (shells in this case), and the result compared to verify that no shell introduced a trusting trust attack.
https://gist.github.com/alganet/1513d7b6abef5c1a53a324d897c3...
Ouroboros self-hosting. They can self-host one another.
The idea is to make shell.c compile from an even simpler C compiler, such as M2-Planet:
https://github.com/oriansj/M2-Planet
Let me remind you that current stage0 bootstraps tinyc from mes, which is an interpreted lisp. It's not that different from the shell architecturally.
The current stage0 also features kaem as one of the first dependencies. kaem is, in fact, a simpler version of the bourne shell.
It's always a tower. You'll never get a one single clean dependency pass in bootstrapping.
This project reminds me of:
The Design of a Self-Compiling C Transpiler Targeting POSIX Shell - https://dl.acm.org/doi/10.1145/3687997.3695639
It's not just a toy or a fun hobby project, there's potential for practical use as a step in bootstrapping an entire software stack from human-verifiable artifacts.
See also pnut.sh, but the server seems to be down at the moment.