ECLiPSe [L1 ] is a Constraint Logic Programming (CLP) system based on Prolog. Besides a bi-directional interface to C/C++ it features a Tcl/Tk interface for embedding or remote connection which is also used to build the integrated development GUI tkeclipse.
ECLiPSe is an open-source software system for the cost-effective development and deployment of constraint programming applications, e.g. in the areas of planning, scheduling, resource allocation, timetabling, transport etc. It is also ideal for teaching most aspects of combinatorial problem solving, e.g. problem modelling, constraint programming, mathematical programming, and search techniques. It contains several constraint solver libraries, a high-level modelling and control language, interfaces to third-party solvers, an integrated development environment and interfaces for embedding into host environments. (cite of the official website)
Some famous examples, that are solvable faster in ECLiPSe than in Tcl:
A lot more examples for the work with ECLiPSe can be found on http://eclipseclp.org/examples/index.html