The counter is counting down to 05/05/15 10:47:00 GMT+0.

Fans of the "Half-Life 1-in-Half-Life 2" fan modification Black Mesa may find themselves with an unexpected treat in the next few days. The official website for the project has started up a mysterious timer which is counting down to 05/05/15 10:47:00 GMT+0.

The most likely explanation for the countdown is that the promised Steam retail version of the game is imminent. The retail version of the game has received a serious makeover since the free version first released back in 2012.

Unfortunately for fans waiting to play Xen, the final chapter of Half-Life that was absent from the initial release of Black Mesa: Source, the developers have stated that it also won't be included in the initial release of the retail version, and will instead be added at a later date. What it will have, however, is a brand-new multiplayer. Yes, you heard right, Half-Life deathmatch is coming back!

So while the Black Mesa team has not confirmed what the countdown means, the retail release of the mod is our best bet. Of course, they could surprise us by releasing Xen for free the mod first...

Source: Black Mesa Source