TattooDB-Android - https://github.com/joelmartinez/TattooDB-AndroidTattooDB is a simple document-oriented database for Android. It uses plain old java objects, and manages it's persistence behind the scenes using SQLite. I wrote it as a response to the ever increasing complexity of ORMs which, ironically, are supposed to make our interactions with a database easier.
I'd like to eventually write versions of this for C# and Objective-C
I have built some samples (emitters, rain, tiles) to show some of the sample code, in addition to some documentation. Eventually, the engine will be refactored to support multiple renderers in addition to canvas, such as WebGL.