Texas Instruments graphing calculators

In the mid-1990s, held a virtual monopoly on s in the academic sector. Most models supported third-party applications using a native as well as the entry-level, and finished programs could be imported from a PC via  rather than transcribed manually. These factors combined to foster internet file-sharing communities wherein many well-known games received TI calculator clones, including Doom.

None of these were true ports, even after the source release, owing to hardware limitations (the popular TI-83 for example had a 6-MHz processor, with 24K ROM and 32K conventional RAM). The standard approach was to superimpose crude imitations of Doom sprites on a wireframe background representing walls and floors.

Doom83
A relatively polished assembler release for TI-83 and TI-83+, supporting multiple weapons, multiple levels, savestates, and OS multitasking. Later remastered as zDoom (no relation) to run on the TI-84+ as well.

Doom89
Somehow this program draws recognizable grayscale reproductions of techbase walls, Doom's title screen, and an intermission screen. It also features keys and a primitive automap. It runs on the TI-89, TI-92+, and Voyage 200.

Doom Collection
This TI-82 game had nine levels, and actually supported mods via a separate program which could edit the bundled levels in place.