I Fast Different
I built an IOS (Android soon) app for alternate-day fasting. It's 100% free, requires no login, keeps all your data with you, and looks / functions nicely (if I do say so myself, since I use it daily). There's also an Apple Watch version.
Anyway, I'd be grateful if people used it and shared any feedback on improvements, bugs, etc. You can download it from the App Store on your iPhone. It is under the name "I Fast Different".