Want to read your Kindle books on your Nook or your Kobo? You can do so using the Kindle for PC app and applying a hack.
It works using a Python script that automates the retrieval of the key from the Kindle book and uses a script to decrypt the content. The above video from TooSmartGuys explains how it works and how to do it.
You can convert one book at a time into a .mobi file that can be transferred to and read on multiple devices.