Octave.app 8.4.0 release!
Special Installation Instructions - REQUIRED!
TL;DR: Use xattr -c to un-quarantine the DMG before opening it.
After downloading the DMG, before opening it (double-clicking it) to do the installation, you must first "un-quarantine" it. Open Terminal and run xattr -c ~/Downloads/Octave-*.dmg. Then you can double-click the DMG file and proceed to install it as usual. If you don't do this extra xattr -c step, it will probably just give you an "app is damaged" error instead of launching when you try to run it from /Applications. Sorry; working on fixing this, but not super hopeful. See #244 – App "damaged" for GitHub downloads.