searched and filtered by tag. In addition, the site provided groups that users could join themselves or by invitation. Groups were typically labs, institutions, professions, or research areas. On line CiteULike entries could be downloaded to a local computer by means of export functions. One export format was BibTeX, the referencing system used in TeX and LaTeX. The BibTeX output could also be imported directly into Overleaf. The RIS file format was also available for commercial bibliography programs such as EndNote or Reference Manager. It also allowed import into the free Zotero bibliography extension of Firefox. Export was possible for individual entries or the entire library. CiteULike gave access to personal or shared bibliographies directly from the web. It allowed one to see what other people had posted publicly, which tags they had added, and how they had commented and rated a paper. It was also possible to browse the public libraries of people with similar interests to discover interesting papers. Groups allowed individual users to collaborate with other users to build a library of references. The data were backed up daily from the central server. Software CiteULike was written in Tcl, with user contributed plugins in Python, Perl, Ruby and Tcl; some additional modules were written in Java; data were stored using PostgreSQL There was no API but plugins could be contributed using Subversion. The software behind the service was closed source, but the dataset collected by the users was in the public domain. About the site The site stemmed from personal scientific requirements. The initial author found existing bibliography software cumbersome. CiteULike was created in November 2004 and further developed in December 2006, running until March 2019. The site was based in the UK. The service was free and was run independently of any particular publisher with a liberal privacy policy. See also Reference management software Comparison of reference management software Social media References External links Library 2.0 Social bookmarking websites Reference management software Social information processing Internet properties established in 2004 Social cataloging applications Internet properties disestablished in 2019