Very attractive physics game. Shadowing effect is very cool! I just fiddled with source code (sorry) and added more cross-platformability and some shortage. The mechanics and appearance remained exactly the same:
<canvas id=c><script>i=Math;X=[];Y=[];c=c.getContext`2d`;h=x=150;y=75;M=z=k=0;onclick=e=>{X.push(e.x-10);Y.push(e.y-10)};t=setInterval(e=>{with(c){fillStyle='#2221';fillRect(0,0,300,h);for(j=0;j<X.length;j++){d=X[j]-x+.1;z+=i.sign(d)*6e-3/d*d;d=Y[j]-y+.1;k+=i.sign(d)*6e-3/d*d;fillStyle='#cc0';fillRect(X[j],Y[j],3,3)}fillStyle='#fff';fillRect(x+=z,y+=k,5,5);v=i.sqrt(z*z+k*k)*10;M=v>M?v|0:M;fillText("MAX: "+M,5,19);if(x<0||x>300||y<0||y>h)clearInterval(t)}},16);</script>