Black Mesa, the re-imagining of Half-Life 1 from Crowbar Collective, has entered Steam Early Access.
At present, 85% of the campaign is complete with around 10 hours worth of gameplay. Early Access users will be helping test the multiplayer deatmatch and team deathmatch modes via six maps as well as the single-player portion.
As will all Early Access titles, upon release the game will automatically update to the release version for those who purchase it for $19.99/£14.99.
You can find out more Black Mesa through Steam.