Total Chaos, a large total conversion mod for Doom II, is now available as a free one-click installation on GOG.
The free mod runs on the GZDoom source port and turns Doom II into a standalone survival horror experience set on “Fort Oasis”, a remote island once run by a community of coal miners who suddenly disappeared, leaving behind an abandoned concrete jungle.
This is a total conversion modification for Doom 2 that operates through the GZDoom source port. It’s now accessible as a GOG One-click Mod. The mod features survival horror gameplay set on Fort Oasis, a remote island known for its abandoned concrete jungle.
Across nine chapters, players explore the island, uncover its mysteries and fight back with improvised weapons like tire irons and pickaxes. Note: a copy of Doom II is required to play.

More details, screenshots and the free mod installation are available on the GOG store page.
Source: GOG