BuddyPress.org

That reminds me of Lester Chan’s Post Ratings plugin – https://wordpress.org/extend/plugins/wp-postratings/ as well as this other one https://wordpress.org/extend/plugins/vote-it-up/ , but both are for posts and the latter one is reported broken.

What good about Lester’s plugin is that you could call the highest rated posts in a page via template tags or using the widget in sidebar http://lesterchan.net/wordpress/readme/wp-postratings.html