Internal Share Feature

Does anyone know of a plugin that allows internal sharing of posts/topics/blogs/statuses/etc? Similar to Facebook's share feature, Twitter's retweet feature, or Tumblr's reblog feature? Currently it seems the only share options are to external sites, and no option for internal unless you copy the link and make a new post that way, but I'd like my users to be able to just press a button and a window pop up with the content they're sharing and an option for a caption/message when sharing it. Tags/prefixes being implemented would also be awesome.