opensoundcontrol.org an Enabling Encoding for Media Applications

The original 1998 implementation of many features of OSC, in C. It has now been superseded by more modern, complete, and usable implementations (at least in the opinion of OSC-Kit author Matt Wright).

The license is compatible both with Gnu systems and with commercial, closed-source systems; the relevant paragraph is "Permission to use, copy, modify, distribute, and distribute modified versions
of this software and its documentation without fee and without a signed
licensing agreement, is hereby granted, provided that the above copyright
notice, this paragraph and the following two paragraphs appear in all copies,
modifications, and distributions."