Sparrow was recently snapped up by Google and people continue to have mixed feelings about this sell-out no one saw coming. The Sparrow team made it clear in a blog post they would cease work on new features (apart from minor updates) as Google has tasked its newly acquired team with improving Gmail mobile apps.
Today, the Sparrow team announced plans to open-source parts of the Sparrow apps for personal use only. If you're good at reverse engineering, why not take a closer look at the Sparrow code?