It's a rare delight to discover that a game you hadn't considered not only has an active modding community, but has one with some really clever boffins doing some awesome work. As is the case with Call of Duty: Black Ops 3, a game that came out in 2015 but is still receiving new workshop content almost a decade later.
Enter TF2 Zombies: A loving recreation of 2Fort (a map so iconic and recognisable in gaming that it's only outdone by Dust) all within Black Ops 3. You can see it showcased by YouTuber FPSpsycho below, though considering the map has 43,520 subscribers at the time of writing and was posted in May, it's been in the ecosystem for a while.
What's really impressive here is the attention to detail—this isn't just an asset flip with a bunch of CoD models gunking the place up. The base game mode has been recreated using TF2 UI assets, all of its models have been swapped, and even the mode's perks—such as the Double-Tap Root Beer or Stamin-Up—have been given their own custom Bonk! Energy drink cans to keep the whole thing in-universe.
The only thing stopping this from looking like a GMOD server or is, invariably, the Black Ops 3 zombies shambling about and the unmistakable feeling of its physics engine. The map itself is a group effort, with a credits list featuring 17 modders (shared below—I'm excluding Valve from that count for obvious reasons) and was produced for the Noahj456 mapping contest.
The contest is the third of its kind, put together by YouTuber Noahj456 who, among other things, seems determined to inject money into modding communities to keep them alive and bumpin'. The bounty for this one was $10,000, with a publicly-available list of entrants including Lethal Company, GoldenEye 700, Arkham Knight and, uh, Spyro 2. I don't wanna think about zombie Spyro, it's too upsetting.
The TF2 map only came 23rd when Noahj456 ranked them, alas, but competition was stiff—with modders recreating The Last of Us: Left Behind, Stranger Things, and Resident Evil 2's Racoon City police station. It's this kind of niche, hyper-specific modding—kept afloat by bands of enthusiasts (and sometimes YouTubers with a lot of money) that makes PC gaming great.