Over the years, it has become a growing trend to get the original DOOM game to run on as many unconventional devices as possible, with programmers in the past being able to get the iconic game to run on a pregnancy test, calculator, thermostat, an ATM, and now an Apple Lightning adapter.
YouTube channel Nylan Satan uploaded a video titled "DOOM running on Apple Lightning to HDMI dongle," which, for those that don't know, is a $50 adapter that's designed to convert Apple's Lighting male connector into a HDMI, enabling Apple devices such as an iPhone, iPad or other Lightning devices to be connected to HDMI-equipped displays. To make the signal conversion, the Lightning to HDMI dongle contains a tiny System-On-Chip (SoC), which runs a very cut-down version of iOS.
Since the SoC is designed to take a video file and convert it so it's compatible with an HDMI signal, the SoC seemingly has enough power to run DOOM. The struggle here would be gaining access to the SoC itself, as Apple, unsurprisingly, has security protections on the device. Once jailbroken, it's then possible to install DOOM on the SoC and, using the processing power of the device, output DOOM onto a display.
It should be noted that playing DOOM on an adapter isn't what most people intend to do, but it's rather a testament to a developer's skill -- and it's just simply cool to see a game that once required an entire PC run on a tiny, unconventional device.