These are the sprites and map tiles for Mozilla's browser-based MMO, BrowserQuest, licensed CC-BY-SA. You guys are awesome! :)
The main art (in browserquest-images) is divided into 3 different sizes in 3 directories (aptly named 1, 2, and 3), and also a common directory for icons, etc.
The browserquest-sprites file contains json files that have animation and state information for each sprite. To be clear, the -sprites file only contains the animation data. All of the actial sprite images are in the first file.