.mobi

MOBI, a MobiPocket Reader file is the extension given to the format that has been developed for the MobiPocket Reader. Amazon uses a descendant of the MOBI file for files created by KindleGen, but renamed to AZW. Originally, MOBI was a format by PalmDOC with certain HTML like tags in the data, a format that is still used by a number of MOBI formatted documents.