I've been using Calibre now for about 3? months and have been very impressed. Calibre runs on the Windows, Linux and Mac OS X platforms. It stores and indexes your ebook collection, will convert ebooks among various formats. All of the information about the ebook is only stored once in the database creating the concept of a logical book. All the major ebook formats are supported, as well as plain text, PDF. From Calibre's FAQ:
calibre supports the conversion of many input formats to many output formats. It can convert every input format in the following list, to every output format.
Input Formats: CBZ, CBR, CBC, EPUB, FB2, HTML, LIT, LRF, MOBI, ODT, PDF, PRC**, PDB, PML, RB, RTF, TXT Output Formats:EPUB, FB2, OEB, LIT, LRF, MOBI, PDB, PML, RB, PDF, TXT
After Calibre converts your ebook to a format compatible with your ebook reader it can sync the format of your choice onto your reader. For me, this means converting ebooks to the MOBI format and then syncing the MOBI format onto my Kindle 1.
Calibre supports SONY PRS 500/505/700, Cybook Gen 3, Amazon Kindle (1 and 2) and the iPhone (with the stanza reader software). Syncing supports updating metadata on the device from metadata in the library and the creation of collections on the device based on the tags defined in the library view. If an book has more than one format available, calibre automatically chooses the best format when uploading to the device.
You don't need an ebook reader to reader books stored in Calibre. Calibre has a built-in content server that allows you to read ebooks through a web-browser.