Thanks! I guess I ended up with the look of that water ring toss game where you mash a button to get a bunch of submerged rings to land on pegs. I do have bigger plans for this game, sound would be a nice addition.

This is my first time making anything resembling a game (unless you like playing with engineering simulations), so I appreciate it! 

I started with a pretty naive implementation where normal/tangential impulses are applied to velocity only, followed by a single position update which integrates velocity at each time step. This probably would've worked better for very small time steps, but at 60Hz it caused all sorts of no-clip issues, balls slowly sinking, balls being pushed through walls by other balls, etc. 

Apparently a solution for this is called sequential impulses, where you update velocity/position multiple times each frame to iteratively separate colliding entities, but obviously it hurt performance (I don't think it helped that I was using float64 for everything either). I ended up just adding a step right before integration where any two objects still intersecting will have their normal velocities clamped to 0 (I only did ball-wall intersections for the submission, but ball-ball also ended up working pretty well).

Your game looks so much more polished and like a game, can't believe you had time to squeeze my game into yours :P