I'm not sure if I understand your question correctly. You are developing an app to collect user needs and you want to know how other do it at the moment ? Is that right ?
In the open source world I've not seen other things than Issues / bugtrackers to keep track of possible improvements.
When working as a freelance I usually go and ask users directly (usually a few users) and put everything in a Trello board. I then use columns and/or labels for additional ordering.
I've not used the new "Project" view of GitLab/GitHub but it seems a very nice alternative to Trello for this kind of workflow.