Jordan Rudess of Dream Theater published a couple apps to the App Store. I'm not sure whether he actually wrote them or served as a product manager and had a contract programmer implement them, but they're pretty cool.
Even more old-school, there's Tom Scholz of Boston, who was an MIT-trained engineer who built his own amplifiers and founded a company to market them. A bunch of his inventions are probably familiar to most guitarists: all Rockman branded pedals and other equipment, the Power Soak and Yellow Jackets to get saturated tube amp sound at low volumes, etc.
Even more old-school, there's Tom Scholz of Boston, who was an MIT-trained engineer who built his own amplifiers and founded a company to market them. A bunch of his inventions are probably familiar to most guitarists: all Rockman branded pedals and other equipment, the Power Soak and Yellow Jackets to get saturated tube amp sound at low volumes, etc.