I just released my first mobile app - aABC for Android devices.
It's written from scratch and does everything on the device, no third-party software or servers used. The initial version only handles melody files (but does try to handle lyrics), later versions will support multiple voices. I know that it would be easy to contrive ABC files that fail to load: at the moment I am simply trying to handle straightforward real-world cases.
aABC is the first piece of software I've not released as open source (cf. GENPO and EWItool), but now that I'm a 'struggling musician' I do need a little return on all the effort.