Xristost blogged about his DIY Audio oscillator with frequency counter project:
After I finished the oscillator, I made some minor changes in the square signal part of the schematic. I connected five of the inverters in parallel with low value load resistors, thus reducing the influence of the parasitic capacitance of the PCB. The goal is to lower rise and fall times of square signal. Max output voltage in square signal mode is around 5V.
Project info at Xristost’s DIYfan blog.