I've been working on my first Mac app for a few weeks and I'm launching it today. It's super-niche and solves a really specific problem: Drawing pictures to an 8x8 LED matrix breakout board from an Arduino. Let's say you wanted to draw a smiley face. In code, that looks like this:
Doing this by hand is obviously a pain. With Matrix Pen you just click to draw, like this: Matrix Pen is $5. You can read more about it here and buy a copy here.