BuddyPress.org

I don’t know of anything that will, at the moment, allow for the kind of “rating” you’re asking for here. I assume you’d use BP activity as your ‘ideas’, though you could also have a custom post type (which would require coding).

You might check out BuddyPress Like, which might get you at least part of the way there: https://wordpress.org/extend/plugins/buddypress-like/