Amazon's new Kindle Cloud Reader web app allows you to read ebooks you've purchased via the Kindle store on any device without installing an app to do it, regardless of whether you have an active internet connection.
The new service gives you access to your entire Kindle library and all of the books you've purchased or borrowed, and an embedded Kindle Store so you can make purchases and add books to your library from within the Cloud Reader web app. There's also an iPad-customised version of the webapp that's specifically designed for the iPad's large touchscreen.
On first login, the service offers to set up offline reading, which installs a browser extension that caches books and makes them available without an internet connection. Kindle Cloud Reader currently only supports Google Chrome, Safari for Mac and PC, and Safari for the iPad. Amazon says support for Firefox, IE and other platforms is on the way in the coming months.