The OpenRosa consortium has produced a set of standards and specifications for data collection on mobile devices based on a modified version of the WC3 XForm 1.1 specification. JavaRosa is an open-source J2ME client that runs on low-end 'feature phones' as well as high-end smart phones and Android devices.
In order to increase the adoption of OpenRosa-based tools and devices (and decrease the dependency on 'dead trees') I've created ocRosa as the iOS/Objective-C counterpart to JavaRosa. This project is comprised of an iOS static library (ocRosa) and reference-app (iRosa) that adheres to the OpenRosa specification.
ocRosa is still a work-in-progress: The XForms/XML parser, basic UI and encrypted local storage are complete, however other features such as submitting forms, authentication, GPS tagging are still being actively developed.