Moodle.org has released 3 minor versions of Moodle following their last major release, 2.9. 2.9.1 most notably brings some solutions to the gradebook upgrade issues that have affected some users. Check out the full list of highlights and resolutions at https://docs.moodle.org/dev/Moodle_2.9.1_release_notes#Highlights.
Over a dozen minor bugs have also been fixed in this release, from UI improvements for IE users to formatting of plaintext emails from forum emails.
Please note that Moodle 2.7 branch is no longer supported for general bug fixes at this time.