Patrick Prosser <pat@cs.strath.ac.uk> discusses various standard
algorithms in the journal Computational Intelligence vol 9(3), 1993.
Scheme versions available from Pat on request; Lisp implementations are
available from <ftp://ftp.cs.strath.ac.uk/local/pat/csp-lab>.

Peter Van Beek <vanbeek@cs.ualberta.ca> has written a set of libraries
for C. This package is available from
<ftp://ftp.cs.ualberta.ca/pub/ai/csp> where you will find a README and
also csplib.tar.Z.

Screamer
<http://www.cs.unh.edu/ccc/archive/constraints/systems/screamer.html> is a
constraint library for Common Lisp.

Michel Lemaitre has written a Common Lisp library dedicated to the
resolution of "Valued Constraint Satisfaction Problems" (for a
description of VCSP, see
<ftp://ftp.cert.fr/pub/verfaillie/ijcai95.ps>).  The library has been
designed with efficiency in mind. It includes Branch and Bound
extensions of the Backtrack and Forward checking algorithm as well as
the "Russian Doll Search" algorithm described in
<ftp://ftp.cert.fr/pub/verfaillie/rds-aaai96.ps>, and several benchmark
problems.  The library is available at
<ftp://ftp.cert.fr/pub/lemaitre/LVCSP/>.