Calibre is available for Windows, Mac OS X and Linux, and is an open source and free eBook management and conversion utility. On its own, Calibre cannot remove DRM from eBooks. DRM stands for Digital rights management. DRM is a set of access control technologies that restricts individuals to use copyrighted works and proprietary hardware.
Digital rights management technologies are in place to try to control the modification, use and distribution of copyrighted works. In order to read DRM protected books on Calibre, Calibre must first be installed. After Calibre is installed onto the reading device, the DRM removal plugin must be downloaded, which will allow DRM eBooks to be accessed.