Other 100% decompilation projects include Ocarina of Time, The Minish Cap, and Super Mario 64.
After more than three years of work, the ZeldaRET team has perfectly recreated the codebase for The Legend of Zelda: Majora's Mask. This is a huge achievement for the Zelda community, enabling not just further study of how the code works, but also ports, mods, optimizations, and hacks for speedrunners.
Project completion has been hovering in the high 90s for six months now, but ZeldaRET member darkeye made the official 100% announcement on Twitter earlier this week. They still noted that there's plenty of work to be done, removing false matches and adding more documentation.
If you're unfamiliar with decompilation, it's the painstaking process of reverse engineering the compiled code in the original cartridge into readable code. Typically, this involves a lot of trial and error, writing and compiling code, and then comparing the results to the original.
Importantly, the goal of this project is not to create a functional port of the game. That would be copyright infringement. Instead, it creates an executable that can be combined with a (legally acquired) ROM of the game. It combines the new code with the copyrighted assets like text, sprites, and textures from the original game. Other groups can use this to make ports, but the ZeldaRET group does not want to be involved.
This is particularly important for consoles like the N64, which is notoriously difficult to emulate. With a perfect codebase, native ports can run smoothly on relatively weak hardware with support for widescreen outputs, higher framerates, cheats, savestates, and much, much more. It also allows code historians to understand why certain glitches happen in a game.
More recently, static recompilation efforts have largely automated the decompilation process, creating native ports in just days or weeks. However, this skips the step where the code is readable by humans, so optimizations and mods are more difficult to implement. This is how the recent Android Majora's Mask port was created.
Previous titles with 100% matching decompilations include Super Mario 64, Ocarina of Time, and The Minish Cap. The ZeldaRET team is currently working on Twilight Princess, Skyward Sword, and Breath of the Wild, but they are years away from completion.