Nintendo Ultra Simulator

The Nintendo Ultra Simulator (or UltraSim in short) is a proprietary Nintendo 64 emulator created by Silicon Graphics approximately in mid 1995. This emulator was handed over to select developers in order to provide a testing environment for them to test their games in while the Nintendo 64's hardware was still a work in progress. Something notable about UltraSim is that it makes use of the simulators present in the Oman Archive. The simulators known to be implemented are the algorithm simulator, the I/O simulator, the co-simulation, the reality display processor simulator, and the reality signal processor simulator. According to the Oman Archive, these simulators are designed to be fast, bit-accurate, and as clock-accurate as possible. UltraSim has never been found and no screenshots or footage of this program in action have surfaced online. Remnants of it are present within the Oman Archive, but the full emulator is nowhere to be seen.

Speculation
In the Oman Archives, there is a folder within the 'TOOLS' folder called 'EMULATE'. Contained within it is the source code for a Nintendo 64 emulator developed by Silicon Graphics. People suggest that this is a high-level version of UltraSim, but there is no evidence to support these claims. UltraSim was meant to be a low-level Nintendo 64 emulator, so the idea of this SGI-made high-level Nintendo 64 emulator being UltraSim is debatable.