Currently, to implement a custom task, you have to extend DefaultTask, which is in the internal package, or implement all of the Task interface. We should provide a public API which makes it easy to implement custom tasks. For example, we could simply move DefaultTask into api.task package and document it. It might also be nice to provide a mechanism where task implementations can be simple POJOs (or POGOs) which do not implement Task, and Gradle adapts them to the Task interface.