You can download, install, and develop under the 5.0 branch, but features are still changing on a daily basis so be prepared for the unexpected. Most of the work is being done in feature branches, and once reviewed are merged into the 5.0 core branch...
Centric CRM 5.0 features are currently being merged and made available in the following subversion repository:
https://svn.centricsuite.com/webapp/branches/branch-50-community
To download make sure you have a user account on the www.concursive.com website, then use your credentials to checkout branch-50-community.