Zavala is an outliner written for Apple platforms by Maurice Parker. It is an open source project and will be free forever. You can find the source code for Zavala on GitHub.

Credits

I would like to thank John Gruber and Brent Simmons for inspiring this project. Their dedication to outliners and disatisfaction with the current generation of them is ultimately what got this project going. In fact John tweeted this:

I would kill for a good simple outliner that synced across iOS and Mac, and had a great simple UI on all three platforms.

If there was a mission statement for Zavala, that would be it.