Cassowary is an incremental constraint solving toolkit that efficiently solves systems of linear equalities and inequalities. Constraints may be either requirements or preferences. Client code specifies the constraints to be maintained, and the solver updates the constrained variables to have values that satisfy the constraints. Version 0.50 of the solving toolkit adds support for a one-way finite domain subsolver.
This package is a port of the original work by Greg Badros and Alan Borning. More information can be found at the following locations:
http://www.cs.washington.edu/research/constraints/cassowary/
http://sourceforge.net/projects/cassowary/