I like NetBSD sh's nextopt <https://github.com/NetBSD/src/blob/23fcbd850aae17ef0843523f3...>. Since getopt's internal state can't be reset portably, most shells roll their own option parser.

Plan 9’s ARG(2) [0] macros are worth a look too. No dependencies at all, just plain macros, super lightweight and easy to use.

[0] https://9fans.github.io/plan9port/man/man3/arg.html