Putting Team Fortress 2 inside Half-Life 2, Lambda Fortress is coming to Steam

The big cross-over mod Lambda Fortress that puts the Team Fortress 2 mercenaries into Half-Life 2 and other Source campaigns is coming to Steam. More goodies thanks to Valve releasing TF2 code into the Source SDK.

I'll admit I must live under a rock when it comes to certain bigger Valve game mods, because I've never heard of it until now and it sounds hilarious. From the Steam page:

Lambda Fortress is a mod for Team Fortress 2 that brings the mercenaries to the gritty world of Half-Life 2 and other Source Engine Campaigns! Play solo or cooperatively across iconic worlds with a unique twist.

Fight your way through City 17, have a lunch break on the coast, or race to White Forest all with your friends!

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Features:

• Singleplayer and Multiplayer Co-Op Play!
• Support for many Source Engine campaigns and map packs!
• Supports Team Fortress 2 Inventories, bring your TF2 items into Lambda Fortress!
• New Weapons!
• Steam Workshop add-ons!
• Additional weapons, game modes and campaign support over future updates!

For it to work you'll need to have Team Fortress 2 and Half-Life 2 installed. No release date has been announced yet.