A dedicated group of fans has excavated a Doom mobile game from the sands of time and made it playable again. You won't find 2005's Doom RPG on the App Store or Play Store: it actually predates iOS and Android by a couple of years. And while Fountainhead Entertainment looked into bringing Doom RPG to Nintendo DS around the time of its original release, the game was exclusively available on Java- and BREW-compatible handsets. Until now.
A small group of developers in Costa Rica going by the name of GEC.inc reverse engineered Doom RPG and got it to work on Windows. Although the port is free to download, it doesn't contain any of the original files you need to actually run the game.
As Ars Technica points out, you'd technically need to have the game installed on a compatible, still-working phone that might be old enough to vote if it were a person. You'd also have to find a way to extract the game files from said device and convert them. On the other hand, you may be able to find Doom RPG by alternate means. You'll still have to convert the files to make the game work, but that seems to be an easy process.
Doom RPG has clear ties to the rest of the series. John Carmack, the lead programmer of the original Doom, was the game director. The game features the protagonist of the first three Doom titles (dubbed "Doomguy" by fans). But instead of rampaging through levels and mowing down monsters in real-time, Doom RPG adopted a turn-based format.
It's always great to see enthusiasts finding ways to preserve games, especially a relatively obscure one that's part of such a famous series. Perhaps for their next trick, the folks at GEC.inc will revive Doom RPG II. Although you can still buy that game from the App Store, it's not compatible with recent versions of iOS. According to the store listing, however, it will run on a Mac running macOS 11.0 or later as long as it has an M1 chip.