#Mastodon v2.4.0rc2 is out: https://github.com/tootsuite/mastodon/releases/tag/v2.4.0rc2
Still some stuff to be done before it can become 2.4.0. In particular, we're adding a webhook-like API so apps can better implement push notifications. This is an extension of the Web Push API we already had implemented, it just needs some cleaning up because previously the events sent through that didn't need to be documented and only the webapp used them.