Google's software suite for combinatorial optimization
ConstraintSolver in Julia
ECLiPSe Constraint Logic Programming System
SOLVESPACE is a free (GPLv3) parametric 3d CAD tool.
SONNET (integer) linear optimisation in .NET
Volunteer workshift scheduler for a helpline service
Solver with Applications in Computer Network Systems Design
A Z3-Based String Constraint Solver
DisChoco: Distributed Constraint Reasoning Solver
JBernstein: Exploration techniques for non-linear constraint checking
The easiest C++ way to deal with constraints !
Processor Enhanced Robust Core Solver for Recursive Multibody Dynamics