calibre is a feature-rich e-book library management application with a variety of useful functions including viewer, addendums, editor, online book and news search/download. The software can perform detailed searches, convert e-books to device-specific formats, batch metadata tools, and a content server for online access to your collection.
The program syncs automatically with many different physical devices. It supports a variety of ebook and document formats.
Cross-platform with clients available for Mac and Linux. Alternatively, Calibre Portable and an outdated X-calibre, as well as a WinXP-compatible version are also available.