Did you actually think Black Mesa was vaporware? Think again.
BlackMesaSource.com now has a countdown available which appears to coincide with the mod's release. Several signs—including this letter—point toward it including the first 14 chapters while excluding Xen, a section that many don't have happy memories of. The countdown ends on September 14th at 8:47am MST which also happens to be the time stated during the introduction of Half-Life.
Black Mesa is a volunteer project that aims to recreate the enthralling world of Half-Life within the much more capable Source engine. Although a Half-Life: Source was released in 2004, it made no visual improvements to what was already considered a dated game at the time, and thus Black Mesa was born. You can expect to see ragdoll physics, improved textures and character models, as well as more believable facial animations.
Since its announcement almost a decade ago Black Mesa has gone through some revisions, mostly by incorporating new versions of the Source engine. This is quite possibly the most ambitious gaming mod of all time, and that alone should earn your attention if its price tag of zero wasn't enough. I'm hoping it'll be downloadable through Steam, and since it will attract attention to Valve's Half-Life universe it's likely, but no confirmation has been made.