The FREE Kindle Reader app is available for just about any device you can think of, and thanks to Amazon’s Whispersync you never have to worry about losing your place in a given Kindle book as you move from device to device! So long as your devices have WiFi or cell connectivity, Amazon’s Whispersync will keep track of where you left off every time. So you can start reading on your Fire, then head out to work and pick up where you left off in the book on your smartphone at lunchtime, and when you’re home from work, get right back into the book on your Fire!
The app is also available for other devices like tablets (even the iPad!), and can be used on both Apple and Android devices. Just click the above link to get full details, and to download the version(s) needed for your specific device(s).