The first custom single-player episode for Black Mesa, a recreation of the HL1 demo Uplink, has just been released.
"Black Mesa: Uplink is the recreation of the Half-Life demo (HL: Uplink) released by Valve in early 1999. The demo featured content that was scrapped from the original storyline. Some might consider it canon with the story, others don't. What matters though, is that many people enjoyed this short episode and that's the reason why I created Uplink for Black Mesa, the long awaited Half-Life remake for the Source Engine."