The extension EXT:tea, is based on Extbase and Fluid. The extension features a range of best practices in relation to automated code checks, unit/functional/acceptance testing and continuous integration.
You can also use this extension to manage your collection of delicious teas.
This extension should not be used as a base for building your own extension or used to blog in a live environment.
In the TYPO3 Core, the system extension EXT:beuser has backend modules based on Extbase. It can therefore be used as a guide on how to develop backend modules with Extbase.