I'm struggling to find any of them now, bit I think there's many sites that provide a toy and interface similar to what you describe.
One in particular, I recall, provided a grid of colourable dots and a minimal language to program them in. There were social features to browse demos people had written. Anyone remember what it's called?
(16 × 16 grid of dots governed by a "shader-like" (?) function getting time, order, column and row indices arguments; negative values red, positive white, zero proximity shrinks.)
Not sure about those "social features", though you can just share the URL with your creating
There's ShaderToy, that works with actual pixels and shader code, but allows some fun effects to be made with very little code: https://www.shadertoy.com/view/4ljGD1 (and some really crazy raymarching stuff to be done by those with serious math/shader skills)
One in particular, I recall, provided a grid of colourable dots and a minimal language to program them in. There were social features to browse demos people had written. Anyone remember what it's called?