I spent some time with Self in the late 90s (at college of course!) and it was impressive on several counts: first, it's JIT compiler allowed Smalltalk to run faster when implemented in Self than without - the same JIT technique was later re-used in Java Hotspots [1]; second, the programming environment was a multi-user environment called Kansas that allowed a whole classroom of students to develop "prototypes" in the same environment (Kansas [2] [3])

[1] http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Self_(p...

[2] http://web.media.mit.edu/~lieber/Lieberary/Softviz/CACM-Debu...

[3] http://bluishcoder.co.nz/2013/09/16/multiple-users-in-a-self...

Except for the part where what Self calls prototype has no equivalent in javascript (constructors are close to Self's `copy` message, but not quite the same) and what javascript calls prototype Self calls mixin (or traits, depending whether they've got ancestors up to the lobby themselves). And a Self object can have multiple mixins and add or remove them at runtime.

Newtonscript was also a descendent. Although I like Objective-C, I do miss Newtonscript and the soup. Prototype-based programming often had a nicer feel than [edit]class[/edit] systems.

http://newtonscript.org - look at the "SELF and the Origins of NewtonScript" down the page