UPDATE: Apple has discontinued support for iPhoto. You can download its replacement, Photos for Mac, by upgrading to OS X Yosemite for free. If you're already running Yosemite, you can download Photos for Mac by checking for updates in the Mac App Store.

iPhoto is Apple's flagship application for managing and viewing photos on your Mac. As a competitor to Picasa it packs a powerful punch as a slick OS X image management app that's fully integrated into iCloud, Maps and more.

Slick well organized interface

The interface is very slick and iPhoto features tons of tools to help you manage your library. In fact, the real strength of the program resides in the organizing options such as organizing by events, create a gallery, print out calendars and books etc. In particular, the unified search function allows you to quickly find any photo based on all sorts of criteria like date, name or keywords and now, even faces.

Well integrated with other Apple apps

Of course, iPhoto is also very well integrated into other Apple apps such as iDVD so your iPhoto images can easily be used in videos that you're editing. Displaying photos in full screen mode isn't as simple as it should be however - it involved way too many clicks and its hard to get rid of the toolbar.

An elegant photo manager