Birdhouse Builder is free. It turns inexpensive cedar fence pickets into sturdy nest boxes, with almost no wasted wood. Everything below works on a phone, right at the saw.
Choose Scout Leader / Nonprofit when you first open the app (free, honor system). You get:
You can stop at any point and pick up where you left off: everything is saved on this phone. The five build steps are numbered on the main screen under BUILD STEPS — IN ORDER.
You can skip this step, but it costs cedar. Without the Knot Hopper, the Picket Wizard treats every picket as knot-free and can't plan around the knots. At the saw you have to spot each knot yourself and work out which parts will fit between them, and any part that ends up on a knot is wasted wood. Mapping takes a few minutes per batch and pays for itself in pickets.