Artelys Knitro is a commercial software package for solving large scale nonlinear mathematical optimization problems.
KNITRO – (the original solver name) short for "Nonlinear Interior point Trust Region Optimization" (the "K" is silent) – was co-created by Richard Waltz, Jorge Nocedal, Todd Plantenga and Richard Byrd.
It was first introduced in 2001, as a derivative of academic research at Northwestern University (through Ziena Optimization LLC), and has since been continually improved by developers at Artelys.
An often easier approach is to develop the optimization problem in an algebraic modeling language.
Knitro provides tools for solving optimization models (both linear and nonlinear) with binary or integer variables.