The Final Hours of Half-Life: Alyx is now live on Steam as a $10 download, and it's a phenomenal look at the underbelly of Valve video game development, told with a wealth of inside access and a host of multimedia goodies.

The project, as led by journalist Geoff Keighley, is a years-in-the-making look at Valve's journey to release a new Half-Life game, complete with stories about other attempts that never got off the ground.

The app's biggest dirt is arguably its confirmation of exactly what started and stopped within Valve on the way to getting Half-Life: Alyx out the door this March.

Inspired by Left 4 Dead, this non-VR version of Half-Life would have revolved around combat sequences through procedurally generated towers and buildings, chained together by crafted plot events.

A more plot-centric Half-Life project emerged within Valve in 2015, led in part by former series scribe Marc Laidlaw: a VR-exclusive game codenamed Borealis.

If that sounds familiar, its concept resembles the story Laidlaw eventually posted for fans, which many took to resemble his vision for a "Half-Life 3." He left Valve shortly after the prototype failed to "gain traction," Keighley writes.

Shortly before ground was broken on what became Half-Life: Alyx, Valve also had a "mini team" begin prototyping a Left 4 Dead sequel in late 2015, which was also shelved after "months of work." (Its codename was "Hot Dog," if you want to start digging through old Source Engine files for hints of it.) And other sections of the app talk about other canceled Valve games, including Left 4 Dead 3 (not to be confused with "Hot Dog") and new, codenamed games like "A.R.T.I." and "RPG." (Today's report also acknowledges a Half-Life 2: Episode 3 project that stalled when its team members shifted to help ship the first Left 4 Dead game.).

Today's news doesn't clarify whether those projects may come back to life, however, and it doesn't exactly say what may happen to In The Valley Of The Gods, a game absorbed as a Valve project when the studio acquired Campo Santo in 2018.