Books
Introduction
An E-book is simply a book that is stored in a computer and read on a computer screen. It is entirely data and does not include any application. This last point is stretched somewhat by recent versions of Adobe Acrobat's PDF reader which can handle embedded Javascript applications in a PDF document. But for the purposes of the OLPC we should restrict ourselves to the simpler, pure data E-book.
Ebook Formats
Ebook formats should be compressed (to conserve space) and open. In particular, they must not be encumbered by patents, and must be inclusive - they should not favor any particular vendor.
DejaVU
The DJVU format was developed in order to provide a much higher level of compression for scanned paper books, than existing formats like JPEG and TIFF can provide.
The PDF format is a simplified form of the Postscript programming language that only includes the commands necessary to paint ink on the page. It is easy to create since one only needs to use the Print function of a word processing or drawing application.
XML and HTML
These are not really E-book formats but they have been used to store E-books, both for special purpose E-book readers and for simply reading through a web browser. The OLPC does include a web browser.
OpenDocument
OpenDocument is a compressed format (zip-compressed XML) for documents, including books, presentations, and spreadsheets. Complex documents (with many images) can be sent as a single document (unlike HTML), yet it can flow in a display (unlike PDF). It is also editable. AbiWord runs on the OLPC and is capable of opening ODF files.
Ebook Readers
Evince
The Evince E-book reader is part of the OLPC project. Currently it supports DJVU, PDF, Postscript and DVI. The OLPC project will likely include only DJVU and PDF as well as an XML/HTML based format. It will also likely have a modified UI targetted to kids.
Plucker
A popular E-book format for PalmOS devices. A reader for Linux/X11/GTK+ already exists in the plkr.org CVS codebase (and is distributed in the Plucker 1.8 source tarfile). It should run on OLPC machine's OS. Most Project Gutenberg books are already available in Plucker format at the URL
http://www.gutenberg.org/cache/plucker/NUMBER/NUMBER
where NUMBER is the PG book number for that book. For instance, John Stuart Mill's autobiography is available from PG in Plucker format as http://www.gutenberg.org/cache/plucker/10378/10378.
FBReader
An open source E-book reader.
OpenBerg
OpenBerg Reader is a multiformat e-Book reader based on Mozilla technologies. It's far from complete but it can already display rich XML/HTML books and organize libraries. Livesearch is in the works, as well as Plucker compatibility. The project could use help.
OpenDocument Viewer
The ODF Fellowship's OpenDocument Viewer could be used as a reader for OpenDocument files. Open source.
OLPC Features
There are some pages already discussing how Ebook formats and Ebook readers could be specially adapted to the OLPC.