Socializeer is a social networking app built using Ruby on Rails. You can check the source on Github. Also take a look at the demo deployed to Heroku.
Users can send friend requests
Users can accept or decline friend requests
Accept or decline of friend requests is done via ajax request
Timeline is populated with posts of user friends
Users can post text/images
Users can like/unlike a post(via ajax requests)
Users can comment on a post
Users can change their profile picture
Storage of images is done with amazon s3 bucket