I was going to make a HN clone in Hack, but gave up because there was no real community around the language, I couldn't find decent hosting and documentation was sparse.

It's a good language, especially if you're one of those people who like PHP except for the few irritating things Hack fixes, it just seems like it died before it could get a good community around it.

I will be forever grateful for Hack spurring some huge improvements in PHP from the 5 to the 7 branch when they were pretty compatible with each other.

I just don't see a reason to follow them on this journey since they decided not to be compatible with PHP back in 3.3.

I think Slack does: https://slack.engineering/taking-php-seriously-cf7a60065329

At some point we made sure that phpMyFAQ works on HHVM - but afaik we never really got any feedback that anyone's actually using it, but we're not on the same level of users as phpMyAdmin for example :). And with this direction it will not be advertised or checked any more in the future either.

Wikipedia was (but is moving off now).

What are they moving to?

Plain PHP (php7). As of now they're still on HHVM though: https://en.wikipedia.org/wiki/Special:Version.

Box did and probably still does.

> is anyone actually using HHVM

Aren't Facebook using it?

Besides Facebook...

Some WordPress hosts were using it

But with this release it will no longer be compatible.