1. [primarily MS-DOS] Said of software conforming to system interface guidelines and standards. Well-behaved software uses the operating system to do chores such as keyboard input, allocating memory and drawing graphics. Oppose ill-behaved.
2. Software that does its job quietly and without counterintuitive effects. Especially said of software having an interface spec sufficiently simple and well-defined that it can be used as a tool by other software. See cat.