I love how the Kindle app feels like a tiny personal library in my pocket — it's surprisingly feature-rich for a free app.
At the basics, you get reading with adjustable font size, font face (including Amazon's comfy serif options), line spacing, margins, and orientation. There are light and dark themes, a warm screen tint on some devices, and continuous scrolling or page-by-page reading. Search within a book, jump to locations or page numbers, and see progress with "time left in chapter" or "time left in book" estimates. I use those when I only have a ten-minute commute and want to squeeze in a scene.
On the interaction side you can highlight, add notes, bookmark, look up words with the built-in dictionary, get instant translations, and tap to access Wikipedia or other reference entries. Highlights and notes sync across devices through Whispersync, and you can access your cloud library, download books for offline reading, organize things into Collections, and even link to Goodreads to share or check recommendations. Some books also offer features like X-Ray, Word Wise, or Immersion Reading (when an Audible narration is available), but those extras depend on the specific title.