I am surprised that nobody has mentioned MIPCL (http://www.mipcl-cpp.appspot.com/index.html). This solver claims to be open source under LGPL license (source: http://www.mipcl-cpp.appspot.com/licence.html), thus it is also suitable to be used in non-open-source applications. But what is missing to be really open source is the source code of the solver itself.
Hans Mittelmann very recently (10 Sep 2017) did Mixed Integer Linear Programming Benchmark: http://plato.asu.edu/ftp/milpc.html (you might also be interested in looking at the overview page http://plato.asu.edu/bench.html or the slides of his talk: http://plato.asu.edu/talks/informs2017.pdf).
In the Mixed Integer Linear Programming Benchmark with 12 threads and a time limit of 2 hours MIPCL managed to solve 79 instances. Only the commercial solvers CPLEX, Gurobi and XPRESS managed to solve more under the given constraints (86 or 87 instances, respectively).
Also in terms of the chosen performance metric (again using 12 threads) MIPCL is faster than the benchmarked SCIP derivates (FSCIPC, FSCIPS) and the open source solver CBC. Again only the commercial solvers CPLEX, Gurobi and XPRESS outcompete MIPCL significantly in terms of performance.
