IDO (IRIS Development Option) by SGI was used by developers creating games on SGI hardware, including studios like Rare and DMA.
While multiple versions of IDO exist, only two versions appear to have been used for N64 development: IDO 5.3 and IDO 7.1.
Since IDO is a compiler designed for the IRIX platform, it does not run natively on modern machines. Early decompilation projects, such as Super Mario 64 and most of Ocarina of Time, relied on running IDO through QEMU, an emulation layer. However, this approach had several drawbacks:
To improve performance and portability, community member Emil began working on statically recompiling IDO ("recomp"). This effort produced a significantly faster executable that could be compiled to run on any modern system. Today, this recompiled version is the primary way IDO is used in most decompilation projects.
The recomp project can be found here, with releases available here.
The "holy grail" of reverse engineering a binary is full decompilation, and that applies to IDO as well. A decompilation effort is currently underway. Unlike most other decompilation projects, a significant portion of IDO is written in Pascal, alongside C. This makes it one of the first matching decompilation projects for Pascal.
The matching decompilation project can be found here.
The following is a list of known projects that use this compiler: