BuddyPress.org

I am not sure I fully understand what you’re asking, but the BuddyPress theme is a great starting point. Users can still choose their own theme (provided you’ve installed and enabled them). On Testbp.org the user profiles use the BuddyPress theme while the blogs use the default WordPress theme.

The BuddyPress theme can also be deconstructed so you can integrate the features you want into a theme of your own to further customize your community’s look and functionality.