Stackoverflow is a social Q&A website. It recommends questions to users who are interesting in the topics of the question based on the tags in user profile.
This article is related to user privacy. Users' trajectory is an important information as an input in location recommendation systems. However, because it is a sensitive data, it should be protected w.r.t user privacy.
This mobile app is a social news aggregator that has recommendation engine and adaptive representation features based on your interests (in user profile). It collects implicit feedback from user interaction with the app and integrated this information o user profile.