Now you don't need a Kindle eReader to buy and read the 360,000+ books Amazon sells in its annoyingly proprietary Kindle format. The desktop app supports color photos, multi-touch pinch-zooms, and displays notes/highlights marked on Kindles and the iPhone.
As for the Mac version? We're still told that's coming soon. [Beta Download | Press Release]
Kindle For PC Features:
• Purchase, download and read hundreds of thousands of books available in the Kindle Store
• Read the beginning of any book for free before you buy
• Access your library of previously purchased Kindle books stored on Amazon's servers for free
• Read books in full color including children's books, cookbooks, travel books, textbooks and graphic novels
• Choose from more than 10 different font sizes and adjust words per line
• Add and automatically synchronize bookmarks and last page read
• View notes and highlights marked on Kindle, Kindle DX, iPhone, and iPod touch
• Zoom in and out of text with a pinch of the fingers (Windows 7 users only)
• Turn pages with a finger swipe (available in a future release for Windows 7 users)