Xrefer
xrefer is a subscription-based online encyclopedia. It provides online versions of around 50 published references works, including both general and specialist dictionaries and encyclopedias.The site was originally free as in beer, supported by advertising, and was one of Wikipedia's main competitors as an open access encyclopedia. When the dot com bust caused Internet advertising revenues to collapse, xrefer sprouted a premium subscription variant, called xreferplus. On the 17th of June, 2003, the gratuit "xrefer showcase" service was discontinued
