I write the code, build the worlds and test everything myself before it goes out. Three things are finished enough to put in front of people.
Connect a rowing machine over Bluetooth and your strokes drive a single scull down a real river. Five routes, a pace boat or a coach who talks to you, interval sessions you write yourself, and other rowers out on the same water. Free.
Air traffic control as a puzzle rather than a reflex test. Sequence arrivals and departures a turn at a time, around runway closures, weather and the occasional go-around. Every board it deals can be solved; the generator will not hand you a dead end.
A Texas BBQ trailer. Smoke the brisket overnight, set the menu and the prices in the morning, then work the lunch rush in real time and find out what you got wrong. Keep at it and you can trade the truck for a building.
Everything here is built solo, in my own time, and tested on the hardware it is meant to run on. The art and audio are licensed from people who make it properly and credited inside each app.
If you use one of them and something is wrong with it, I would rather hear about it than not: info@nchanted.eu. Waterline has its own contact page for feature requests, support and account deletion.