Its a poor mans function generator, with max 5v p-p, it can generate sine,triangle, square and sawtooth wave forms http://black-electronics.com/blog/arduino-waveform-generator/
A waveform generator is an essential tool for any electronics workbench, previously I made a square wave generator, which was ok for testing digital circuits, Now want to make projects which would require a function generator. Also was stripped for cash. The cost of this is around Rs.500. May be I'll make a better one using special function genator ICs, Ofcourse you will see it here when I do.
Among electronics there are two groups(IMHO) analog dudes and digital dude. I belong to digital dudes. I learned how a DAC works, which is nicely explained here http://www.pyroelectro.com/tutorials/waveform_generator/theory.html
On mechanical side
I've read this many times on the internet "Measure twice cut once". I made a mistake while drilling holes, since its for my personal use, I let it slide. But I'll definately keep a note on all cutting and drilling holes "Measure twice, cut once"