TOMS917 is a C++ library which evaluates Wright's Omega function, by Piers Lawrence, Robert Corless, David Jeffrey.
The original, true, correct version of ACM TOMS Algorithm 917 is available through ACM: http://www.acm.org/pubs/calgo or NETLIB: http://www.netlib.org/toms/index.html.
The computer code and data files made available on this web page are distributed under the GNU LGPL license.
TOMS917 is available in a C version and a C++ version.
TOMS443, a C++ library which evaluates Lambert's W function. This is a version of ACM TOMS algorithm 443.
TOMS743, a C++ library which evaluates Lambert's W function. This is a version of ACM TOMS algorithm 743, by Barry, Barry and Culligan-Hensley.
Piers Lawrence, Robert Corless, David Jeffrey.
You can go up one level to the C+= source codes.