Okay. Google doesn't offer Picasa for the Mac. Why? Because we don't need it! If you purchased your Mac over the last few years or you've purchased the awesome iLife package ($74US Retail), then you already have iPhoto. iPhoto does everything Picasa does and quite a bit more! (Can Picasa work with RAW files?).
This Instructable is the Mac answer to' fabulous, but Windows-centric Quick and Great Photo Editing with Picasa. To be fair, we will just import a picture, straighten it, color correct it, crop it and resize it in under a minute. While there's a great deal we could do more, this just shows the procedure to duplicate on the Mac what was done on a PC with Picasa.
Note: Like all of my Instructables, this one was done entirely using iPhoto, Preview and Mac OS X's built-in screen capturing features. Okay… Some of my Instructables have diagrams that were created in Appleworks or Eagle.
Step 1: Nothing to download!
Step 2: Import a picture
If you're working with a photo from the internet or off of a memory card, just drag it to the iPhoto icon in your dock. It will self-import.
Step 3: Rotate and Get Lucky
To rotate, just click the Rotate button in the lower left of the window. If you hold the camera the other way around, hold the Option (Alt) key to rotate in the other direction
The Retouch feature is great, but in order to work, you need at least some white in the picture. My backdrop wasn't white, so the effect is minimal.