Voice-based data collection.
At Aquaya we were helping to collect water quality data from a variety of communities. There was a survey component and it had to be localized. There was typically a simple app to mediate this, but in Cambodia the phones couldn't support the Khmer language.
So I made this voice-based system. You could call in, hear the questions and give your responses via voice. The surveyors would do this for a variety of locations and time-points. Back at the web portal you can transcribe (and maybe translate) the responses. I think you could record questions via voice or maybe you had to do that on the web portal.
This one definitely had connections to one of my other projects, Meduele.
The code is gone, alas, but would be easy to recreate! IIRC I wrote most of it in one day during a conference.