ActionCable is a Rails-specific implementation of web sockets that allows users to chat with each other live.
Geokit Rails is a Rails gem that contacts the Google Geocoding API to find users' locations. In the search algorithm, it considers all of the things important to a DnD player in addition to if the found users are within the distance the person making the search is willing to travel to (and if the found user is also willing to travel as far as the person making the search is located).
Dicer supports the ability to add friends and block users to make the social experience it creates more enjoyable and safe for everyone.
Dicer allows users to connect to Facebook to see if their friends are also on Dicer. If so, these friends are added to the user's friend list to make finding other DnD users even faster.
Except for a few uses of Bootstrap's column system, Dicer does not rely on any CSS framework to style its pages.