What fish in 7 gallon?

Im trying to convince my mom to keep the empty 7 gallon tank (it was her old tank but she upgraded it to a really big one). Since we have all of the stuff we need, expect plants I feel like it’s gonna work. I already have 2 Bettas so I’m kinda looking for anorher type of fish, anyone have advice for what fish I can put in there? (If I’m allowed to keep the tank ofcourse)