I worked on several vertical and in-house apps for the Newton platform back in the day. I was at the launch in Boston and the first couple of development conferences. Landon Dyer's work and Walter Smith's work on the object store and the NewtonScript language implementation was amazing. It had some performance and practical issues and bugs, but developing for the thing was largely a joy -- the closest I've come to the live coding and debugging on a dynamic runtime that people loved about the original Lisp machines. I've always felt that we would have been better off with a NewtonScript 3.0 than either Java or JavaScript. JavaScript in particular -- it was like the basic ideas of NewtonScript implemented badly by people with no taste and a "kitchen sink" approach to language design.
Along with Apple Dylan, the platforms were really ahead of their time. Going back to Objective-C felt like such a huge step backwards. And now I'm developing primarily in C and C++ and still wishing for something better. I satisfy my not-so-secret longings by writing Haskell in my spare time...