Project 64 was a project dedicated to the historical preservation of Commodore related manuals and documents. The project started in June of 1995 by Chris Berneburg and was continuously updated for nearly a decade by Berneburg and others. The last updates to the site date from 2004.
There have been some independent attempts to revive the project such as Project 64 Reloaded which appears to have stalled.
In July 2018 Ruud Baltissen needed a file from the original C64.org link, only to find out that the whole site had disappeared. With some help he found a mirror from 2015 and decided to host it in his own site: Project 64. This is not a direct link because he has no idea yet if there are any legal issues involved by using this mirror. To be more precise, using the layout made by Dean Thompson.
If you want to contribute, use the email address found on Ruud's site. New contributions will be added from the end of August due to the holidays he deserves.
Ruud is also thinking about hosting ROMs or other binaries that go with already hosted documents. That is, as long as it is legal.
Ruud will also provide a ZIP file that will contain a mirror of Project 64. Main reason: if for what ever reason something happens to this site, it will be much easier to restore it for another volunteer.