1. I would put REST api as a separate section, and also not in the same hierarchy/section as client libraries, because REST is part of the project, and clients consume it.
2. Having sections named "clients" and "client libraries" can be confusing. Perhaps "integrations" or "applications that consume hawkular" is better for "clients"?
3. Is there a section dedicated to community events (meetups/conferences/hackaton/summit, etc.) where there are talks about the project? Didn't see it in the diagram.
4. Overview can link to quick start imo
5. What should be the difference between quick start and the download sections?
6. Ways to contact community? I saw only social links in the footer, but what about mailing list/irc,etc.?
p.s. I wrote an article couple of years ago on usability of community websites, maybe some ideas from there would be helpful as well
https://opensource.com/business/14/8/open-source-project-front-door