UltraHLE is a Nintendo 64 emulator, and is acclaimed to be the first emulator of the system. The first (and last) version was released in January 28, 1999.
The focus of UltraHLE was not to run every game of Nintendo 64 with accuracy, it was made to run specific games with the best compatibility, such as The Legend of Zelda, Mario Kart, etc, and such, some obscure games might not work.
The drawback is, the emulator requires an 3dfx based video card, and its not gonna work without it. Though, it may be a good choice for old toasters.