Alternatives? You want more?
Here's a few:
Naked light.[Beta] Non-destructive image editing. Node-based compositing. Live filters. High-end tools. And infinite resolution. It's image editing, re-invented.
Other than Version Tracker you might try MacUpdate which has sales from time to time:
You want more? Here's a couple of my favs:
http://mac.majorgeeks.com/ (Has Windows listings too)
Find open source software alternatives to well-known commercial software: (all platforms)