Silicon Graphics Indigo 2
The 4th machine from Silicon Graphics (SGI) and the third with the new 64bit MIPS-CPU. These very costly machines ($89000 to $139000 depending on configuration) were 3D workhorses thanks to the RISC-architecture and the powerful videocards.
So powerful, that the Indigo2s are used to render the 1995 movie Toy Story (3D-animation). The machines run IRIX, a UNIX-clone, that is capable of clustering the processing power.
The purple ones are the most powerful, these use the MIPS R10000 (10K) CPU. The green ones were available in multiple configurations (starting with the R4400 to R10K)