I have been waiting with bated breath for OpenMandriva Lx 4 to go stable. But now, when I go to openmandriva.org, I get a 404 error (yesterday it was 505) -- but when I go to forums.openmandriva.org, everything works.

A few weeks ago, June 6 was the proposed date for the stable version. As of now, there is nothing on the website (at all!, except for forums, which do not address the issue), and one magazine has written that it will come "summer or early fall", with no reference to a source.

So is OM4 still coming, or did they run out of money for the website, or what?

The Wiki is still up, also. The GitHub link still works with updates as recent as tomorrow (I'm guessing the site is on UTC as there is an update dated June 11, 2019, whereas it's still June 10 where I sit).

Websites have been known to break, as I can testify from personal experience.

ondoho, that is a new one on me!