Bootswatch - Free Themes For Bootstrap

Bootswatch is an easy to use free themes for Bootstrap
 
Easy to Install - Simply download a CSS file and replace the one in Bootstrap. No messing around with hex values.
 
Customizable - Changes are contained in just two SASS files, enabling further customization and ensuring forward compatibility.
 
Open Source - Bootstrap themes are released under the MIT License and maintained by the community on GitHub.