OSoft, Inc. have released my book 'A Byte of Python' in Thout format. There are two aspects of Thout - one is that the Thout format is based on XHTML and second, the Thout reader software (similar to Windows
.chm Help Viewer) is available for all the major platforms. I am excited about this because Thout provides some very cool functionality - for example, users will soon be able to "upload/download public notes that are placed at the point in the documentation the comment refers to".
There are currently three Python books in Thout format at the OSoft website - the official Python documentation, my book and 'Dive Into Python'. There are lots of books in the other categories as well.
Btw, Thout software is OSI-certified open source, so it's good to know that the Thout format itself is implicitly open as well.