Users of Excel should also be aware of OpenSolver. This is an Excel VBA add-in that extends the Excel built-in solver from Frontline Systems Inc. This add-in allows the user to formulate a model using the builtin Excel solver. However, rather than optimize the model with the built-in Excel solver engine, with the OpenSolver add-in, you can solve the problem using the COIN-OR Cbc mixed-integer linear programming solver. Thus, there are no size limitations based on license restrictions. Students can build and experiment with large realistic-sized models. Another feature of OpenSolver is that it has a command, View LP Model, which shows the algebraic statement of the model. This is a nice feature for debugging and actually seeing the underlying constraints and objective function in an easily readable format. Although built on COIN-OR software, OpenSolver is not available at the COIN-OR website; it must be obtained at http://opensolver.org/.
Martin, Kipp: Tutorial: COIN-OR: Software for the OR Community, Interfaces 40(6), pp. 465–476, INFORMS 2011
http://interfaces.journal.informs.org/cgi/reprint/40/6/465 (subscription required)