[3] Couenne is an implementation of a branch-and-bound where every subproblem is solved by constructing a linear programming relaxation to obtain a lower bound.
Branching may occur at both continuous and integer variables, which is necessary in global optimization problems.
It requires the input to be specified in A Mathematical Programming Language (AMPL) .nl format, so as to be used from AMPL, and writes as an output a file .sol containing the best solution found until that moment (if the optimization is interrupted) or the global optimum if it completes without interruption.
The development of Couenne began in 2006 within a collaboration between IBM and Carnegie Mellon University.
The source code is available for download in the Computational Infrastructure for Operations Research COIN-OR repository and on GitHub.