This week's Steam Marketing message has word that beginning this week, Steam will begin offering modifications, or MODs as they put it. Word is: "The first five MODs to ship on steam will be Age of Chivalry, D.I.P.R.I.P., Insurgency, Synergy, and Zombie Panic. As always, owners of any Source game will be able to download and play all of these MODs for free." Mods hosted on Steam will also use Steamworks for stat tracking and other community integration.