Diode shaping + LPF acting on the triangle wave.
You can build a square-wave oscillator using a capacitor, a resistor and a
> couple of gates. Fit that to a ramp generating op-amp, and you've got a
> triangle wave. That's two of the three functions one of these things can
> produce done for less than a fiver. That just leaves sine-waves - they
> can't really be done with a lashup