Links to various repositories of some maybe less well known constraint solvers. This is mainly so that I can find them again.
A C++ version minicpp of MiniCP developed by Laurent Michel and his students. It is mainly used for research. It has a FlatZinc parser.
Another version of minicpp that includes Haddock a system for using MDDs for propagation.
The Glasgow Subgraph Solver developed my Ciaran McCreesh that includes support for proof logging.