VideLibri lists the books you have borrowed from a public library and lets you search the library catalog from your local device. It has all the usual features of a library OPAC, i.e. viewing, renewing, searching and ordering books. It also renews all due books automatically and can do other things only a locally running app can do, like keeping a history of all ever borrowed books across multiple libraries. Developed since 2006 it is the world's first library app, and by supporting 20 different kinds of OPACs from different vendors it is compatible with more libraries than any other app. So far VideLibri has been tested with 200 libraries successfully, but it was designed to allow every user to adds its own library without requiring any/much programming knowledge. For this purpose three query languages were developed that are supposed to simplify the querying of webpages as much as possible:- A pattern-matching language that selects arbitrary data from a single HTML page, based on an annotated sample of that page. - A catalog of related pages to apply these patterns to multiple webpages. Its syntax is similar to XSLT and likewise it is almost Turing complete (i.e. it has the necessary control structures, but requires XPath to do calculations ).- A dialect of XPath/XQuery/JSONiq that is Turing-complete and thus can calculate arbitrary, unexpected things.VideLibri is platform-independent and currently there are binaries for (Desktop) Windows, Linux and Android.