Black Mesa (formerly known as Black Mesa Source) is a mod for the Source engine. It's a remake of the original Half-Life. And, well, at this point we really should refer to it as a game instead of a mod, since it uses all-new textures and models developed solely by the mod team. As I understand it, there is close to nothing in terms of art remaining from Half-Life 2. The project was started in 2004, and I've been waiting since 2004 for it to be released.
Just today (I know this because I check it everyday), the website for this mod has undergone a huge overhaul (which is really just a new home page design). It's sexier now. Not much in the name of new content, and it still hasn't been released, but the website is definitely giving yours truly a mountain in his pants.
Now, the devs have promised that this brilliant mod will be unveiled to the public at some date in 2009. This is better than the original proclamation that it would be released "when it's done" or "when Hell freezes over." So now we find ourselves dealing with the tragedy of only having awesome wallpaper photos to keep us busy. But there's a mere two months left in the year, so expect for an update as soon as I get my hands on it. Oh, and this thing's gonna be free. Did I mention that it's gonna be free? It will be. Free.