Xiph's reference implementation is called opus-tools, and it consists of a separate encoder and decoder; it is published under the terms of a BSD-like license.

It is written in Java and published as free software under the terms of the GNU General Public License (GPL).

This X-Plain module is published by the Patient Education Institute and licensed by the National Library of Medicine under the following terms of use.

It is published as free software under the terms of the GNU Lesser General Public License version 2.1 or later.

It is being published as free software under the terms of the GNU General Public License (GPL).

The released parts were published under the terms of the GNU General Public License, a free software license.

Dalvik is published under the terms of the Apache License 2.0.

All Pathfinder books are published under the terms of the Open Game License (OGL).

The original implementation was written for Windows by Ben Rudiak-Gould and published under the terms of the GPL.

Later, the software was rewritten using C++ and the Qt framework and published under the terms of the GPL v3.