Just like Apple's Mac App Store, which is how the company sells both its own and third-party Mac software, Amazon users can redownload applications if they somehow misplace the file. However, unlike with Apple's offering, there's no mechanism to keep applications up to date--something Amazon has left up to software makers. Some applications are also bundled with DRM or serial number authentication, the latter of which is not a concern on the Mac App Store.
So far there's already a handful of software that cannot be found on the Mac App Store, including Microsoft's Office for Mac 2011, which is being promoted heavily. Microsoft has long offered it as a digital download through its own store, but not on Apple's Mac App Store.
As part of the store launch, Amazon is offering buyers a $5 discount on any Mac game or software purchase through June 1, 2011.