I don't have an iphone, so I don't know for sure if the app is available for IOS, but I use ReptileBuddy and I LOVE it! It keeps track of the days since last feeding for you, displays weight updates in a graph, and keeps a history of things like shedding and enclosure cleanings. It has little features on top of those that I use a lot, like a little notes function for each animal, and you can store pictures and scans of documents for each animal. It also has breeding project logs and a genetics calculator, but I don't breed reptiles so I can't attest to how good they are. It does make you upgrade to a paid account if you want to keep multiple feeding schedules, but honestly since it displays a "days since last feed" log for each animal it helps me stay on top of that anyway without upgrading. I had a quick look and I think the app is available on IOS.