bookend is a free Android app developed by iDOC K.K. that allows users to view e-book content from the bookend service. The app is compatible with Cloud Library, which enables users to share their e-book content with Windows, Mac, and iOS bookend applications. Additionally, there are several sample contents available from the "Store" menu.

It's worth noting that an internet connection is required during the first startup and to use the Cloud Library. In some cases, users may need to install additional viewer applications to read specific contents. Overall, bookend is a useful e-book viewer app for Android that provides easy access to a variety of e-book content.