A square wave output with just 2 more resistors.
I'm not sure how much current is available from the suare wave output. It could be increased, but it's remarkably sensitive to the input to the second transistor. There's a narrow band where it works; on either side it fades out or locks up due to positive feedback. It seems to be OK with loads under 10kR provided the upper resistor of the 3 is changed to compensate.
