CREDIT: SIMPSONSDOOM
Homer’s had enough in this mod of Doom.

As with any form of consumable media, there's a certain inevitability that a game continues to enjoy popularity years after its release, whether for purposes of nostalgia or simply because it tickles the fancy of people seeking out that niche. Mostly hidden out of sight from the mainstream gaming press, these games still continue to live on through their modding communities and general fandom.

Planescape: Torment
The '90s truly was a golden age of PC RPGs. It was the decade that gave us the still-beloved Fallout series (of course, in a much more different shape than the bloody, visceral real-time FPS-RPG it is today) and various Dungeons and Dragons-based story games like BioWare's (rest in peace) Baldur's Gate games. However, one DnD-based RPG still continues to enjoy a certain amount of popularity: Planescape: Torment.

The butt of a running joke, P:T is described by snarkers as the best game they ever read, and they aren't all wrong either. The game has a LOT of reading (if you opt to skip the even lengthier voiceovers), be it conversations between the player and NPCs or simply the game instructing you on play. Despite having elements that makes P:T a poor game but a decent fantasy novel, it enjoys immense popularity with a modding community. If you wish to play this game today on a modern computer, it'll be impossible, or, at least, would've been if it wasn't for the various fan patches and fixes released that makes the game work perfectly. There's of course a lot of fan-made DLC, either cut content restored or new sidestories.

Doom
If you don't know what Doom is at this point… well, I won't sugarcoat it for you, that's pretty sad. It's like not knowing what Pong or Donkey Kong is.

The revolutionary demon-blasting FPS that became a cultural phenomenon is far, far, FAR from being dead. There's various ports available for Doom that are constantly in development — Zdoom and Skulltag just to name a few. And the mods, the fan maps, the servers (everything, really) all still going in full steam.

There's nothing esoteric about the Doom scene today; you can easily download Doom and play some of the various mods for it, be it the beloved Chex Quest games, or the... transgressive comedy mod, Grezzo 2.

S.T.A.L.K.E.R.
It's the little Ukranian game series that could; S.T.A.L.K.E.R. as a series of post-apocalyptic hardcore open-world horror RPGFPSes (read this slowly) is as well-loved as it is chock full of bugs. Fan patches, total transformation mods, cut content restoration, you name it. All three S.T.A.L.K.E.R. games have mods that make it easier for newbies (or make it even more difficult).

The open-world nature of the game coupled with the naturalistic random encounter system makes for many forum threads filled with keyboard adventurers swapping stories about the time the bloodsucker in the distance nearly tore them to shreds.

Postal 2
Ohhhh boy. If there ever was a game that defined niche appeal, it'd be Postal 2. A game that, simply put, was designed to offend everyone. EVERYONE. The game was panned by the mainstream gaming press for that very reason, and yet, the no-holds-bar approach it had was what made it such an enduring icon of cult gaming. Once again, kudos to the modding community for releasing various weapon packs and fan DLCs.

A game about a trailer park resident going about his daily chores, the game, hilariously enough, is playable without committing a single act of violence, placing any potential for wrongdoings entirely within player choice, a rather interesting bit of social commentary in itself.