Ebooks can be read on your computer, tablet, or phone. No special devices needed.
That’s right, you don't need a Kindle to read Kindle/mobi ebooks.
If you download the free Kindle app you can read Kindle books directly from Amazon and you can read mobi format books. The app is available for the computer (Amazon account, Kindle cloud reader- you can download and read books directly from Amazon on your computer), and the free app is available for all android and iPhone devices.
You can also email files directly to your device. You can find your device's email address under your Amazon account "manage your content and devices", click over to "Your devices" and it will show your device's email address. You can email a mobi file directly to the device. If you have a pdf you can email it to the device with convert in the subject line and it will convert it to a more friendly reading format.
Epub format ebooks can be read on your computer by downloading the free program Adobe Digital Editions.
You can also download Universal Book Reader which supports epub formats so you can read them on your phone or tablet.