Intel Paragon XP/S 140 (#1 on the top500 list in June 1994): 143.4 GFLOPS [2]
Don't know whether to marvel at how fast a modern smartphone is, or how "slow" old supercomputers were.
(Yes, I realize GFLOPS is probably not the best comparison and I have no idea where gadgetversus.com even gets its numbers from, but I think they're at least in the ballpark).