calibre - Ebook manager, viewer & converter
draw.io - Online diagramming application
FBReader - FBReader is an e-book reader for various platforms. Features:
LucidChart - LucidChart is the missing link in online productivity suites. LucidChart allows users to create, collaborate on, and publish attractive flowcharts and other diagrams from a web browser.
Google Play Books - Google Play Books lets you search, preview, and buy millions of books using Google Book Search.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.