If you’ve developed a plugin or theme and want to get a jump start on testing that theme against the changes that will be released in Moodle 2.9, the 2.9Dev branch is for you and is available now. This non-production-ready version of Moodle’s future major release is available almost two months in advance of the mid-May launch date.
Download it for testing here: https://download.moodle.org/releases/development/
If you’re interested in the fixed issues that will be released with Moodle 2.9 (enhancements, bug fixes, etc.) the full list of 200+ is right here.
One enhancement that I think is pretty cool: New page that shows all browser sessions of a current user (a bit of a security and user authenticity enhancement).
