Something is happening over at BMRF.US, a website associated with the Source-based Half-Life remake Black Mesa: Source. The site is repeating an emergency broadcast warning of "a disaster of unknown type" that has occurred at the Black Mesa Research Facility, and ordering the immediate evacuation of everyone within 75 miles. Half-Life 3 confirmed?
Well, no, I think we can safely say that's not it. But the warning may have something to do with a coming launch of Black Mesa: Source as a stand-alone game on Steam. It was originally released as a free mod in 2012, and in late 2013 was among the first games to get the Greenlight on Steam—a somewhat surprising development, given that it's based entirely on Valve's intellectual property.
It's generally assumed that when the commercial launch rolls around, it will include the Xen levels, which weren't included with the original mod. According to a post on the Black Mesa: Source forums, however, one of the developers said the alert "has nothing to do with the imminent release of Xen," but added that more hints may be in the offing.
It's worth remembering that the BMRF site was actually part of the Black Mesa: Source ARG that launched shortly after the mod was released, and as noted by Reddit, the site is owned by the Black Mesa web developer. It's legit, in other words, but legit what, exactly, remains a mystery.