An online encyclopedia is an internet-based structured collection of knowledge, inspired by the concept of traditional paper encyclopedias. Different types of online encyclopedias exist. Distinctions can be made, e.g., in terms of technical platform, subject focus, editing rights, license or intended audience. Citizendium, for example, is wiki-based, open for all subjects compatible with family-friendlyness and use in primary education, editable by any registered user, uses a Creative Commons CC-by-sa 3.0 licence and targets basically everyone who can read online. Other online encyclopedias include Wikipedia, Encyclopaedia Britannica, Encyclopedia of Cosmos, Encyclopedia of Earth, Encyclopedia of Life and Scholarpedia.