There are two that I’ve used and found quite useful – OnTrack and BG Monitor. They each have pros and cons, but I’m using BG Monitor at the moment as I like the charts it produces, and it gives you nice rolling averages. I also like the layout of the data input screen, and the ability to add notes to things. The OnTrack one gives you longer averages, and has the ability to track more things (like weight, BP etc), but I wasn’t really using them much.
Both free 