Calibre is a cross-platform, open-source library for your e-books that can also sync them to your e-book reader. Available for Windows, Mac, and Linux, it offers a massive range of individual book customizations, as well as format conversion and newspaper-style RSS feed grabbing, but lacks a slick interface that would go a long way toward convincing skeptics that it's a powerful tool.

Calibre's lackluster interface is nevertheless replete with features. (Credit: Screenshot by Seth Rosenblatt/CNET)

The number of things that Calibre can do for your digital book collection is stunning. You can view books in a basic spreadsheet layout or with an adaptation of Apple's Cover Flow. Cover Flow here lacks a default image, and the sudden white rectangle where the book cover should be is jarring. It can be toggled with the big, white arrow icon in the bottom-right corner of the main window--an equally awkward placement.

You can add books, convert formats, and edit metadata on the fly. Much like the metatags for digital music, you can choose a cover of your own liking. If you have the ISBN number of a book in the metatag, there's a helpful button that will grab the cover from the Internet. You can also choose a cover that you have stored locally. Other metadata includes author name, book name, search tags, publisher, rating, series, reader comments, and available formats. Calibre manages multiple formats of books under one book name, so it's easy to sync the Mobi to a Kindle without having to confuse it with the EPUB or PDF version you've stored locally.

Calibre's metatag editing window. (Credit: Screenshot by Seth Rosenblatt/CNET)

Calibre converts most major formats to EPUB, MOBI, or LRF, and only syncs the appropriate format when you initiate the transfer. It also has default settings for comic book formats, and can convert CBZ and CBR with ease. Converting comics takes longer since they're images. When I synced a CBZ that I created (made of random JPEG files) to the Kindle 2, Calibre inserted a blank page in-between each legitimate image. They also appeared in a reduced size and I needed to zoom in to see details more clearly, but the implications for portable digital comics are clear.

Calibre also comes with a default desktop e-book reader, accessible from the View button, so you can check out your books without having a device. The navigation buttons for the reading window pop up on the left of the pane, clearing screen real estate and making the application useful for lightweight Netbooks--a smart design move, given that the portable reading device market is still wide open.

Calibre also has a killer feature: it manages RSS feeds into a newspaper format. Currently, it supports just under 100 English-language feeds in this style, including various tech news, general news, and niche market Web sites. There's even XKCD.

As I noted earlier, the only major drawback in Calibre is that the interface, with its oversize buttons and primary-colored icons, lacks the gloss that the general public has come to expect from digital library programs like iTunes. Fortunately, Calibre is open source in an untapped market and has already received one minor update since I found out about it last week, so its development trajectory could be strong.

If you have an e-book reader and you try out Calibre this weekend, let me know what you think about it in the comments below.