EPUB (electronic publication) is an e-book standard, by the International Digital Publishing Forum (IDPF), which consists of three file format standards (files have the extension .epub), described below. It supersedes the Open eBook standard.
http://en.wikipedia.org/wiki/EPUB
There is a portable compiler eCub available.
https://portableapps.com/node/9219
There was a project to portablise FBReader although no action has been taken for some time. I would be happy to test as I read copious amounts of eBooks and desperately need a portable reader.
https://portableapps.com/node/10150
https://portableapps.com/node/11807
Otherwise I would be happy to hear of any projects or even plug-ins or add-ons for other portable applications that would enable me to read this format. The standard has great possibilities but NEEDS a portable viewer! It seems strange to me that OpenOfficeOrg isn't compatible (a topic I will be bringing up in their forums.) There was a plugin for Firefox but it is incompatible with current releases and numerous request for updating have been ignored.
Regards