The result of what Nintendo and Sony accomplished in the time the companies were working together is most likely sitting in front of you, the PlayStation. From an SNES add-on to the most popular console on the market - this is quite an evolution, indeed. But Nintendo was determined to penetrate the add-on scene. It wasn't possible to start development on one for the out-of-date SNES, so the N64 became the target. The outcome? The 64DD (Disc Drive).Only a very small number of 64DDs were released in 2000.
Which isn't surprising if you know anything of its development. It should be noted, however, that Nintendo shifted its aim and hopes for the 64DD from being a mass-market machine to an experiment, if you will. But should you track one down? What titles are worth getting? These, as well as many other questions, will be answered.