re2c is a tool for writing fast and flexible lexers. A re2c generated scanner is usually 2-3 times faster than a flex based scanner, and its input model is much more flexible.

Various GNU tools and software for Win32 including ports of bison, byacc, and flex

A general-purpose parser generator that converts a grammar description for an LALR context-free grammar into a C program to parse that grammar. [Open source, GPL]

A fast lexical analyser generator. It is a tool for generating programs that perform pattern-matching on text. There are many applications for Flex, including writing compilers in conjunction with GNU Bison. [Open source, GPL]

All about Lex, Yacc, Flex, and Bison: Overview, Online Documentation, Papers, Tools, Pointers

Very simple LALR(1) open-source parser generator. Outputs C, claims to produce faster parsers than yacc/bison.

A parser generator for Haskell.

Tutorial in Lex and Yacc, tools that simplify compiler construction.

An object oriented recursive descent parser generator framework implemented using template meta-programming techniques. Expression templates allow to approximate the syntax of Extended Backus Normal Form (EBNF) completely in C++.

Compiles FSMs from regular languages into executable C, C++, Objective-C or D code. The GPL'ed software can be used to create a parser for any language that is regular. Examples include parsing Unix mailbox files and general lexing tasks.