Game does not work

I just downloaded Black Mesa and when I go to play it, a Steam error pops up and says it failed to start (missing executable) I want to play this so bad and I don’t want to wait for Steam to release it. Please help:’(

Did you follow the Installation Manual? If you did, check out the Troubleshooting FAQ.

Founded in 2004, Leakfree.org became one of the first online communities dedicated to Valve’s Source engine development. It is more famously known for the formation of Black Mesa: Source under the 'Leakfree Modification Team' handle in September 2004.