There is, of course, PCRE.

I know also of Olin Shiver's Structural Regular Expressions, and Rob Pike's Structural Regular Expressions.

I also understand that Raku's regexps are different from perl's implementation

Are there other ways to express regular expressions? Like, is there a syntax based on Object Oriented Programming? Concatenative Programming? Visual ways to represent the action of the regexp?

I'm thinking of a list of answers like this one for visualizations of lambda calculus by prathyvsh

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    $\begingroup$ Historically in the Unix world there was grep syntax and lex syntax. Grep syntax has spread far and wide, while the less horrible lex syntax has been largely forgotten. You could also look at parsing combinators in Haskell, though they're far from limited to regular languages (but then neither are PCREs). $\endgroup$ – benrg Feb 7 at 8:20