Callisto is a free WordPress Theme. The theme comes with four different flavors, namely; Blue, Red, Green and Gray. The blue color comes by default.
Callisto WordPress Theme is highly search engine optimized and Google Adsense optimized. Callisto has two widget ready columns/sidebars, Left and Right sidebars.
Features:
- 3 Columns
- Web 2.0 Looks
- Widgetized Sidebar
- SEO Optimized
- Dynamic background
- Four unique colors (Red, Green, Blue, Gray)
- Social Bookmarks Integration
- Better Navigation
- High Content Visibility
- WordPress 2.7 Support
This theme is released under GPL.
Download 
Callisto WordPress Theme.
Great looking theme. Must be very popular. Thanks for the write up!