All Opus+ documentation is available from this page. This is provided for online viewing, but note, that any Opus+ component that you download will always include all the relevant documentation, so you can read it offline as you wish.
There are several documents about Opus+ in the set. An overview of all the main concepts that underpin Opus+ is available here. It is recommended that people new to Opus+ read this first. There is an installation guide giving instructions on how to install Opus+ here. Note that Opus+ is a stand-alone component that in no way registers itself with your computer, or changes its system settings in any way. Java programmers who want to use the Opus+ library can view the javadocs here. All this documentation is covered by the GNU Free Documentation License v1.3