Stanislav Gobunov has FBReader built for Intel Mac (Mac OS X 10.4 or later)
here. There is a thread on
FBReader's Google Group about this and earlier OSX port attempts.
Those with a Nokia 770 or N800 or an iLiad will already be familiar with
FBReader, which now runs on Linux, Windows and Mac desktop systems. It supports many e-book formats (but no DRM), including limited support for the new ePub format (TOC not yet supported in ePub, and CSS and tables not supported in any format). If you are new to FBReader note that it is highly customizable, so if you don't like its default behavior - change it. There isn't much documentation but see
Visual Tour of FBReader.