One way this website is "open" is that all the source files that contain and create the site content are in a world-readable git repository:
https://github.com/CNMAT/OpenSoundControl.org
Therefore you can:
- Clone the site for yourself to download and examine all the files.
- Browse the content of the site within github's website (e.g., this file), but beware: the internal links are to html files but the repo contains only md source.
- Contribute to the site via a pull request (if you know what you're doing). Don't add html files or any implementations/*.md files because these are generated from other files.
- Keep your own copy or mirror of the site content.