Age of Empires 2 has been around for quite a long time now; 14 years by my count. Yet it's remained incredibly popular with a dedicated fan base, a popularity which was boosted by the more recent HD remaster of the game. It's for this version that Forgotten Empires is for. It started life as a fan-made mod, and they've now turned it into an official expansion.
PCGamer reports that Skybox Labs, a group of amateur developers, have brought the mod up to standard. The Forgotten includes five forgotten civilisations and their technologies, some new maps, four new campaigns, new AI, and Twitch integration so people can watch you lay waste to foreign armies.
There's no exact release date just yet, but it's roughly scheduled for a Steam release in September.