The idea of portable apps is to be able to store an application on a USB drive or memory card along with whatever data you need and be able to plug the USB device into any Windows machine and be able to view the data. For eBooks this adds the ability to store your reading application along with the eBooks so you can easily read them anywhere there is a computer available.
There is also a Portable Apps tool that manages the applications present on a USB drive. It provides a menu to launch apps and can also be used to ensure safe removal of the device. It can manage any portable application, not just those built specifically for Portable Apps.
 Reading Applications
- Calibre - See Calibre for a description. Reads multiple formats and can convert formats.
- Cool Reader - can be installed portable. It reads several formats, particularly ePUB and FB2.
- FBReader - See FBReader for a description of this application. It reads lots of eBook formats.
- Firefox portable - add EPUBReader to read ePUB files.
- SeaMonkey portable - can also use EPUBReader for ePUB files.
- AbiWord portable - read RTF and DOC files.
- Foxit Reader - read PDF files.
- STDU Viewer - PDF, DjVu, CBR, CBZ, XPS, FB2 and image files viewer.
- Sumatra portable - lightweight reader for PDF files.
- Java Dejaview - read DJVU files.
- Sword project - Bible study.
- LCDBible - light weight Bible program uses Sword Bible
- BerBible - light weight Bible program with several versions.
- Notepad++ - Powerful text editor.
- Opera - Opera is a Web browser with extensions
 Making non-portable apps portable
JauntePE represents a collection of tools that helps you to make non-portable applications portable by virtualizing access to the filesystem and registry. Download - freeware.