My personal list of dead but influential languages would include NewtonScript [1]:
With the cancellation of the Newton project by Apple in 1998,[8] all
further mainstream developments on NewtonScript were stopped. However,
the features used in NewtonScript would continue to inspire other
programming models and languages.
The prototype-based object model of Self and NewtonScript was used in
JavaScript, the most popular and visible language to use the concept so
far.
NewtonScript is also one of the conceptual ancestors (together with
Smalltalk, Self, Act1, Lisp and Lua) of a general-purpose programming
language called Io[9] which implements the same differential
inheritance model, which was used in NewtonScript to conserve memory.
Not sure why NewtonScript rather Self. Self is the originator of prototype-based programming and differential inheritance (although the term differential programming was preferred). NewtonScript adopted them, as did JS and Io.
