Curious to know the difference between this and what http://www.boost.org/doc/libs/1_64_0/libs/spirit/doc/html/in... (Boost Spirit Lexer Library) provides.

Spirit is a far more extensive library. It supports more than just lexing.

This library is much simpler without many of the features found in Spirit on the other hand it is faster in both compilation times and running times when lexing.