In my opinion, Cool Reader would make a great addition to the portable suite.
CoolReader 3.X is free open-source (GPL) multiplattform eBook Reader under active development.
http://coolreader.org/e-index.htm
Common features
epub (non-DRM), fb2, txt, rtf, html, chm, tcr formats supported
Pages or scroll view
Table of contents
Bookmarks
Text search
Hyphenation dictionaries
Most complete FB2 format support: styles, tables, footnotes
Additional fonts support (.ttf)
Can read books from zip archives
Automatic reformatting of .txt files (auto detect headings etc.)
Styles can be customized in wide range using external CSS
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I was just getting ready to send a similar request. Can someone create ANY .epub PortableApps app. I don't car that much about which one (I have used various Desktop .epub programs) just so there is a good one available. THANKS.
Russ ( PastorDIC @ Gmail.com )
A great reader
PortableApps.com Advocate
Have you looked at Cslibre? https://portableapps.com/node/20518
“Be who you are and say what you feel because those who mind don't matter and those who matter don't mind.” Dr. Seuss
List of most ebook software for Windows
http://wiki.mobileread.com/wiki/E-book_software#Windows
Calibre has a portable version, and will read almost any ebook format including epub and mobi.
https://portableapps.com/node/28898