Fastr is a Flickr-based multiplayer game in which you face off against strangers in real time to guess the common tag for a series of images that are displayed. The faster you guess the tag, the more points you get. Each round lasts for five minutes, with 8 or 10 sets of photos to identify each round. It's fast-paced and addictive fun that requires only wit and a modern web browser and is free.