Apple - What is Application Loader and why does it want to open EPUB?

Application Loader is the app used to publish content you've created on the App Store. In addition to actual Apps, this also includes ebooks in EPUB format. It's part of Xcode and no, it can't display EPUB documents, so you may want to tell OS X to always open your EPUB documents with Stanza again (this association likely got overwritten when Xcode was last updated).

Application Loader is a developer tool (part of Xcode) that uploads apps to the Mac/iOS App Stores for sale.

See this question for instructions on fixing your file type associations.

• How to Change File Type Associations?

According to Wikipedia Stanza is no longer supported: "According to an email received by a member of the Facebook "Revive Stanza" group, Amazon will no longer be updating or supporting Stanza after version 3.2."

I suggest considering Calibre. "calibre is free and open source e-book computer software that organizes, saves and manages e-books, supporting a variety of formats"