The original 1998 implementation of many features of OSC, in C. It has now been superseded by more modern, complete, and usable implementations (at least in the opinion of OSC-Kit author Matt Wright).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