Picasa

Picasa is an image organizer, viewer, and editor, currently owned by Google Inc. and integrated with the Picasa Web Albums service, which allows its users to host their photos on the Web.

After the application is installed on your computer, it automatically starts scanning you data drives, searching for pictures. In case you don't want some of your folders scanned, you just change the scanning settings, and the pictures from there don't get to the application main library.
Since version 3.6 Picasa automatically singles out all faces, found in your pics, and suggests tagging them. The person you tag gets automatically marked on all the photos, where the software recognizes them. This helps immensely, when you, for example, want to upload an album of your kids' prom photos, or want to show your Grandma the photos of you in Venice but can't find them on your hard drive.
Version 3.8 saw two major new features, namely Face Movie and Batch Upload.
The former allows you to combine the slideshow making and face recognizing features of Picasa and create a slideshow presentation, centered around a specific person, in almost no time: a precious option when you've got to work under time constraints.
Batch Upload facilitates your uploading process on Picasa Web Albums, allowing you to upload more than one album at a time. Other than that, now it is possible to better manage your uploaded albums, because the correspoding features like removing, upload size, and visibility, have been greatly in this Picasa release.
Since the application currently belongs to Google, it benefits from integration with other Google services. So, every single picture may be geotagged in Picasa, i.e. the photo can be updated with the data about where it was made. Moreover, you can use Google Maps for this purpose, which increases the reliability of this information immensely.
As for the editing features, Picasa contains quite a great number of various filters, tuning options, and basic fixes. With their help you can change the way a picture look, or remove some of its defects, like red eyes effect. Of course, Picasa is not such a mighty editing tool as Photshop or Gwenview, but its capabilities are more than sufficient for a regular user.
In a nutshell, Picasa is a nice universal image application, allowing you to quickly organize, edit or share your pictures with your friends and other people. In fact, as of today, it is the best freeware application of its kind and a definite must-have for every sociable Mac user.