The Federation of American Scientists unveiled an infrastructure for cataloguing virtual environments called Virtual Worlds. This wiki currently classifies 74 virtual worlds and includes links to tools, news, and other online reference materials. A virtual world is a computer-based simulated environment. Users inhabit and interact via avatars, or computer-generated characters. The FAS Learning Technologies Program built the Virtual Worlds Almanac as a guide for information on the structure and capabilities of these sites. The wiki includes the engines used to create these simulated environments and related information like news, reviews, and other links. Virtual world developers, academics, and the general public who use the listed worlds are encouraged to review and contribute to the wiki. FAS invites all users to create new listings for virtual worlds not already included. There are also forms to upload screenshots, news articles, external links, and more. Most of the data in the Virtual Worlds Almanac is entered via checkboxes, drop-down lists, and specific textboxes, and supported variables include those related to use, technical features, communication, and demographics.