One website that I think could be a good alternative to G+ is Pillowfort.

One website that I think could be a good alternative to G+ is Pillowfort. -Unfortunately, Pillowfort is mostly in beta and to register one has to pay $5 to their kickstarter.
(https://www.kickstarter.com/projects/562544287/pillowfortio-a-better-social-media-platform)

Edit: The kickstarter is over but they accept the $5 donations through their paypal. More information: http://pillowfort-io.tumblr.com/post/178548733326/this-weeks-invites-have-gone-out-if-you-donated

It seems to have it all though. Communities. Threaded comments. Blacklisting. Granular sharing and privacy controls. Private messages. After the crowdfunding phase they intend to have premium account features and the choice for users to opt-in to advertisements.

This can all be read on their Kickstarter. You can also try out the platform as a demo user.
(https://www.pillowfort.io/demo_login)
https://www.kickstarter.com/projects/562544287/pillowfortio-a-better-social-media-platform