This is a free, introductory textbook/course on Spanish. "500 million people today speak Spanish worldwide and it is an easy language to learn for native or fluent speakers of English or Roman languages. The cultures of Spanish-speaking countries are rich in literature, food, music, and the arts. Throughout this course, you will find fact sections that contain facts about Spanish-speaking countries or their cultures." The site operates as a wiki, so it is continually updated by participants.
Via Jon Perkins