Foursquare Trip Tips - Collect and share travel recommendations from friends.
Recombee - Recommender system as a service that uses advanced Machine Learning and Artificial Intelligence algorithms. Easy to try and evaluate.
Likewise - Get recommendations you love, from people you know.
Reddit List - Tracking the top 5000 subreddits
Wayward - Track and share your adventures
reddit shell - Web-based shell for browsing reddit (pretend you're working)