There's one significant change in RC2. As of this release we have switched over to using the Apps module to facilitate the downloading of Open Outreach. This means that the Apps module as well as the Debut Apps connector module are enabled. Apps uses the same technology as is used for installing updates from drupal.org.
For anyone updating for a previous version, running update.php will give you the update to enable the newly created Open Outreach App as well as enabling the necessary Apps modules. You'll now see an additional tab in your toolbar where you can see the Apps that are enabled as well as download new ones.
For the complete technical notes, see the release notes on drupal.org.