It's a bug fix release to version 4.0, with lots of (25 to be exact) bug fixes and updates.
Check for all the details here: https://www.mellel.com/relese-notes-latest/
Or use Check for Updates to download the updater.
... And if you need to, our trusty download page will help you download the dmg: https://www.mellel.com/download/
Ori from Mellel
Mellel 4.0.1 is here
Moderators: Eyal Redler, redlers, Ori Redler