Project Penelope is the offline version of Age of Empires Online.
The project was founded by a community member who released a version of Age of Empires Online from it's beta days which had a scenario editor built in. This editor allowed you to place units, make maps, and gave you a way to play the Age of Empires Online. Now Project Penelope supports the final version of Age of Empires Online and some of it's features.
All six civilizations can be played with the right technologies, units can be customized with vanity gear and even some original quests can be played. All this still in offline mode only.
Learn in this article how to install Project Penelope version 1.2.