Great fun Matteo!
It reminds me of using Aegis Animator way back in the Amiga days.
Some bad stuff though ..
Its difficult to selet a control point in Play mode. The mouse pointer x/y hotspot seems to be off.
Same for draw mode. Its hard to tell whether the mouse click will 'select' a ball which is being hovered over or place a new one. There is no way of telling.
Some of the text is corrupt (chopped off):

Can the window size be adjusted? I cannot see the bottom because I have my task bar set to [always on top].
For reference I'm running in 1024x768.
Suggestions:
mouse wheel to zoom in/out
RMB to delete
set color of ball being hovered over to white