Just as the title indicates. I tried a whole day and spent more than $20, but didn't find a single app that achieves these simplest tasks. I don't need fancy editing/annotating features, just need plain reading. I need djvu because half of my books are in this format. I need multi-tab because when I work, I typically need to open 4--5 books and check back and forth. The vertical continuous viewing is almost natural (especially when you read math books when large formulas could break one page). I don't understand why most apps wouldn't even support this feature.