Hellbound: A 90's First Person Shooter

https://www.kickstarter.com/projects/tobiasrusjan/hellbound-a-90s-first-person-shooter-made-20-years
Steam has the demo. It was fun.

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.