Go Map!! is an OSM editor I maintain for use on iPhone and iPad, available from the App Store.
Version 1.6 was released last week, with the primary improvement being support for multipolygon relations, and much improved protection against accidental damage to relations of all types.
More importantly, I've published the source code on GitHub if you'd like to contribute or use the code in your own project: https://github.com/bryceco/GoMap Building the source requires a Mac and Xcode. Contributing code requires fluency in Objective-C. It is released under the ISC license, the same as iD.
If you are a frequent user of Go Map!! and wish to be a beta tester please send me an email using the app's "Bug Reports and Suggestions" button.
Finally, here's a short video showing basic use of the app: https://youtu.be/GUWg4d-jt5o