The big news is the debut of Team Tournaments, which allow players to form teams and compete for prizes. You can be a part of a maximum of 60 teams; each team will have both an owner and a captain (or captains) that will be able to manage it. The teams feature will initially be available on Uncharted 4, Uncharted: The Lost Legacy, Mantis Burn Racing and World of Tanks. It will be available starting October 5th.
There have also been improvements to the Messages app. Some have already been previewed in the beta release: If you're in multiple group messages, you can leave more than one at once. Additionally, you can share music via the PS4 Messages app. A new feature, just announced today, is a website thumbnail preview for links in messages.
Sony also touts the new ability to follow anyone, regardless of whether you are friends (subject, of course, to individual users' privacy settings). Previously you could only follow a user you weren't friends with if they had a verified account. PlayStation has also updated their Communities app with landscape mode, as well as support for animated GIFs and the languages Czech, Greek, Hungarian, Indonesian, Romanian, Thai and Vietnamese. They PlayStation Messages app has also been updated with stickers and support for the afore-mentioned languages.