Pick a part in the tray, then tap the board to put it there. With a pen or a mouse you see where it will go before you tap.
Tap a part on the board to pick it up: ⟲ ⟳ turn it, ✕ takes it off. Tap it again to turn it.
Press START. The cannon fires the orb. Get it into the reactor and you win.
Fewer parts, more stars. Three stars at par.
Zoom with two fingers, the mouse wheel, or + and −. Drag to look around.
Keyboard: arrows move, Enter places or picks, R turns, Delete takes off, 1 to 5 pick a part, G starts, + − 0 zoom.
Three ways to play
Grid: parts snap to squares and the orb moves in straight lines. Free physics: parts go anywhere at any angle, and the orb falls, rolls and bounces. Chain reaction: a machine that's nearly built; fill the ? squares so each cannon fires the next.