Cheddar is an open source universal iOS application for managing tasks on both iPhone and iPad devices. A few screenshots of the Cheddar application follow:
The cheddar application is based on the Cheddar API, which is accessible using OAuth 2. You can learn more at the Cheddar developer site.
Cheddar for Mac
You can also check out a public beta of Cheddar for Mac.
You can download Cheddar from github.