Use this just like the Pulse UGen - as with SawDPW, this uses the "Differentiated Parabolic Wave" technique to create a waveform extremely efficiently and with low (but not zero) aliasing.
freq - Frequency in Hertz (control rate)
width - Pulse width ratio from zero to one. 0.5 makes a square wave. This cannot be modulated.
This is actually a "pseudo-ugen" based on SawDPW rather than a separate UGen in itself, but is still very efficient. Compare the CPU usage in these examples: