I think your first idea is utter genius. People always have spare seeds and vegetables and being able to exchange currency for them through an app interface in your neighbourhood is very clever.

The last one? Depressing. Management of debt is a very grown-up thing to deal with but the constant reminder of it sitting there on your phone sounds quite damaging to ones' mental health.

Perhaps that last one could only work within 48 hours of your payday and then locks itself up for the rest of the month?