If you don’t allow for automatic updates on Steam, you might want to here, as the newest “free” DLC for Portal 2 is out for PC/Mac.
Known as the “Perpetual Testing Initiative” DLC, the DLC allows you to develop your very own Portal 2 maps easily and to a fair scale; the DLC will download onto your platform (PC or Mac) like a patch. Check out our preview of it when it was in beta here.
The DLC allows you to add turrets, gels, cubes, sludge, glass planes- everything you might expect in a Portal 2 map. Check out one I created earlier tonight (it took me 4 hours), known as “It’s Manic, You Know” by clicking here. But that’s not all, as to celebrate the release, Valve have dropped the price of Portal 2 on Steam to just £5.09/$6.79, so get it while it’s hot!