Holy stuff I'm actually excited when I read the changelog.
I'll list a few of the most interesting ones (to me).
-Added partial work around fix for the "infinite lag" problem
This was a common issue with plenty of players. What this means is that you no longer have to be fetched/admin wanded to stop this "lag".
-getUTF8String function added
This is something that RTB 4 needs.
-Protocol registration so you can join via blockland:// links
This will allow you to join servers via a webpage.
-You can now build inside water bricks
forget yeah.
Though because of this one:
-"too loud" check disabled
I'll have to update one of my add-ons and I wont be surprised to see several topics of why this update didn't work.
Edit: Comment on website:
Looks fancier now, and I bet "Servers" is what was going to replace that blank button originally, till the redesign came in.