One of the biggest problems with Google+ has been its inability to create a group wherein all peers are equal. You can create a hashtag that everyone can post to but you can't control the membership of, or a Page that a few moderators can share to, but it's difficult to add users to (for non-public posts, Pages can only add users to circles once they add the Page first). Communities finally fixes this problem by creating public or private groups that anyone within can share to.
One of the coolest features about Google+ is its ability to automatically upload all the photos you take and then allow you to selectively share them at your convenience. While Facebook has been testing this same type of feature with a few users since August, the service is now rolling out publicly to everyone. As long as you have the most recent version of the Android app, you should be able to enable it soon.
In the mad scramble to keep up with all the major social networks, a number of third-party clients have popped up over the years to help you manage everything. Not that Twitter takes too kindly to these sorts of shenanigans. Still, services like Seesmic tried to replicate the native Twitter experience while augmenting it with Facebook integration in one app. When Twitter gutted third-party APIs for consumer-facing apps, Seesmic likely faced some trouble.