For those that are wondering: they're allowed to release this because it's a mod (so you can only play it if you have a Source engine game installed) and they a

For those that are wondering: they're allowed to release this because it's a mod (so you can only play it if you have a Source engine game installed) and they aren't charging anything. It's higher profile than most, but it's just like any other mod in that respect. They did drop the "Source" from the game title for trademark concerns from Valve. What's funny is that now Team Fortress 2 is free to play, and counts as a Source engine game, so you don't have to pay Valve any money to play Black Mesa. Of course, now you have Steam with all its sales installed, and the likelihood of you wanting to play it without having purchased any of their other games is pretty small...