Social networking (Facebook, Twitter, and LinkedIn) help people cultivate a community of friends and share information.
Blogs = personal websites written by somebody who is passionate about a topic, provide a means to share that passion with the world and to foster an active community of readers who provide comments on the author's posts.
Video and image sharing (YouTube, Vimeo, Flickr, Slide-Share, and Instagram) simplify the process of sharing + commenting on photos, graphic images, and videos.
Chat rooms and message boards serve as online meeting places where people meet and discuss topics of interest, with the main feature being that anyone can start a discussion thread.
Review sites (Yelp, Rotten Tomatoes, Amazon, and TripAdvisor) - places where consumers rate products, services, and companies.
Wikis are websites that anybody can edit and update.
Social bookmarking (Reddit) allow users to suggest content to others and vote on what is interesting.
Mobile applications with GPS-generated location services add the component of identifying exactly where each user is in the world.