A move made so quietly that I didn't even notice until almost a month later, Amazon Kindle software has been available for Mac OS X 10.5 (Leopard) and Mac OS X 10.6 (Snow Leopard) users since the end of March.
The file size is 22MB, a stark contrast to the PC software which is only 5MB.
The Kindle Store has increased a bit in size since the PC release too, now offering over 500,000 e-books for viewing. There appears to be no differences in the releases; the software is just now functioning for Macs.
As a reminder, Brian Jacques books The Sable Quean, Eulalia!, Loamhedge, Rakkety Tam, Triss, Castaways of the Flying Dutchman, The Angel's Command, Voyage of Slaves, and The Ribbajack, as well as the Redwall Wiki News Feed are all available for download in the Kindle Store.
The software is a free download, available at http://www.amazon.com/kindleformac.