A project has already been started to give it some long-awaited documentation, but of course help is needed with that.
ZScript is still not done yet, and discussions about it continue.
That being said, it still does need testing, and you can now find it in the newest devbuilds of any of your favorite source ports:
ZDoom (Windows) GZDoom (Windows) QZDoom (Windows)
ZDoom (Mac OS X) GZDoom (Mac OS X) QZDoom (Mac OS X)
As before, things that need to be tested include mods that use both DECORATE and ZScript code. D4D has already been converted, so test that, too! Bugs go to the same spot as always. (As a note, mods using ZScript are currently locked behind a command-line parameter; you must use -zscript to activate them)
Spoiler: old post