The Yabause emulator carries the torch now. They have all been abandoned (or in the case of Giri Giri, sold to SEGA). There were a string of Windows-only closed-source emulators, including SSF, Giri Giri, Satourne, etc. It was expensive, hard to program for, and its graphical abilities were best suited to 2D.
Before the days of multi-core processors, parallelism meant having multiple chips. The SEGA Saturn was long said to be impossible to emulate, because of its unusual (ridiculous) architecture that incorporated eight processors (two Hitachi SuperH SH-2 processors, one Hitachi SH-1 processor just for streaming and decompressing from the disc in realtime, two “video display processors” from SEGA, a Motorola 68EC000 for sound, another custom SEGA DSP chip for sound built by Yamaha, and finally something called the System Control Unit).
