There are many cool variants. Some variants are:
- Scan and Shop app
- Graphical Restaurant Reservation/Booking app
- On-demand car wash app
- An online flower and gift delivering app
- Finance and bill management app
- Voice language translation app, etc.
For finance niche it can be mobile banking, stock trading, expense tracker, etc. Real examples you can check on https://reinvently.com/finance-app-development/ this company has good experience in this niche.