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.
There is a portable compiler eCub available.
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.
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.