Exercise programs to practice with!

So I'm kinda of an middle experienced Java student and I'm looking for a bigger challenge. I do alot of reading about java and java exercises, I really like CodeWars for example. But I need to take some time of these exercises and I want to write something that does a litte more. I want to practice some OOP concepts and guidelines and not only writing small methods that solve small problems. I want to write bigger applications that I or someone could actually use.

The thing is that I don't have much imagination right now and I'm not sure what to do. Here are some of the programs I have already done:

A simple textbased adventure game
Pacman game with swing(this was a pain!)
Chat client that works over the internet with groups and private like chat
An android alarm app
An android calender/tasker like app
A game with 2 cars racing were pressing keys made them go faster.
A booking system for buses which talked to a database I made.
A Calculator with JavaFX
A Notepad clone

So what I really want is tips/ideas for smaller applications that can do various things. It could be something useful but could also just be a game or really anyhting.