A DIY true
I flipped the frame of my bike upside down, installed the wheel in the front fork, and then attached a ruler (metric, natch) to the fork with elastic bands.
Get the ruler as close to the rim as you can without touching it, then give the wheel a spin. The ruler acts as a fixed reference point against which you can evaluate warps in the rim.
Using the markings on the ruler and the width of the rim, I was able to roughly calculate where the rim should sit. Wherever the spinning rim would "cross the line" I would tighten the group of spokes opposite that point. Sometimes, instead, I would loosen the group of spokes on the same side as that point, in an effort to maintain the overall A440 tuning of the spokes.
After the rough home-true, I went down to Our Community Bikes to finish the job on their more precise truing stands and dishing tools.