Rex is a regular expression library which implements most of the POSIX 1003.2 specification. It is very mature and has been in heavy production use by thousands of users, on many platforms, since 2002.
That project aims at providing a framework around the WSDLPull (http://wsdlpull.sourceforge.net) source code, so as to ease the packaging and delivery processes, allowing to deliver packages for a great number of Linux distributions and Unices.