DeltaBlue is an efficient, incremental local propagation constraint solver. Like most local propagation algorithms, it cannot accomodate cyclic constraints. Our current research is focussed primarily on constraint solvers that do not have this restriction, and we have now released the Cassowary Constraint Solving Toolkit for linear arithmetic constraints.
However, DeltaBlue may still be of interest to some researchers, since it is able to handle constraints over arbitrary domains. Here are links to a comprehensive paper on DeltaBlue, and a code archive:
A current research topic is how to integrate a DeltaBlue-like local propagation solver with Cassowary. If this effort is successful, we will include this code in future versions of Cassowary.