UltraHLE is a Nintendo 64 emulator. It was the first emulator to define and implement high-level emulation; instead of emulating the Nintendo 64 itself, UltraHLE re-implements the programming libraries used by the games it supports.
UltraHLE's only release was in 1999. Its support of many N64 titles so early in the N64's lifespan earned it wide acclaim and notice in the gaming industry and by mainstream media such as a mention on Time Magazine, including by Nintendo themselves who threatened to sue the developers.