Remember the efforts to reverse-engineer Super Mario 64 a while back, which resulted in unofficial ports to systems like the Dreamcast and PS2? Well, a similar project is underway to decompile The Legend of Zelda: Ocarina of Time’s game code, and it's almost finished.
The Zelda Reverse Engineering Team (ZRET) has been working on the project for over 18 months, and the team now claims the venture is 91% finished.
While Nintendo took legal action against those who used the decompiled Super Mario 64 code to create mods and post them online, this kind of reverse-engineering project is perfectly legal because the project recreates the original code from scratch in modern coding languages (in this case, C) without using any of the original copyrighted assets.
Why is such a project a big deal? Well, in the case of Super Mario 64, a host of ports were made available, including one for PC which boosted the screen resolution and opened up all kinds of modding opportunities, such as widescreen mode and ray-tracing.
Such work also preserves the game in a way that means it can easily be made accessible in the future on modern formats, outside of Nintendo's original source code and the various versions of the game (N64, GameCube, 3DS). Decompiling a game in this manner can also lead to new bugs being discovered, which can have ramifications within the popular speedrunning community.
You can follow the progress of ZRET here.