Amazon hasn't released sales figures for the hardware-based Kindle reader, but under pressure from Sony and the new Barnes and Noble 'nook,' Amazon is working hard to increase the share of Kindle users. That means not restricting e-book reading to an Amazon device, but opening up the software to run on more platforms.
Kindle already has a clever e-book reader for the iPhone and iPod touch, and it allows standalone use, or synchronization with a Kindle so you can stop reading on one device and then pick up on the same page on the other.
There's no estimated shipping date for the Mac Kindle software, and we can't forget that if Apple delivers a tablet computer it could put Amazon into direct competition with Apple.
This is bound to be fun to watch.