RE-flex is a regex-centric, fast lexical analyzer generator for C++
with full Unicode support.

Faster than Flex and other regex matchers.  Accepts Flex
specifications.  Generates reusable source code that is easy to
understand.  Easily integrates with Bison and other parsers.  Includes
a fast stand-alone regex engine and library.

It also can use regex matchers from boost or pcre2, as well as
visualizing FSM graphs with graphviz.