Perhaps the simplest software that you can work with is the one that allows you to deal with bank accounts and transactions regarding it. Designing a robust system that allows you to engage in transactions is something that every beginner should get started with.
The proposed system is a web-based project that allows you to do everything a bank would allow you to do naturally. One should be able to deposit money and withdraw money from a particular account as the user desires.
There should be a validation to allow only a particular amount of cash inflows at any time, as well as to allow withdrawals if the balance is sufficient. There should also be the calculation of interest and its addition to the balance every month.
There can be multiple improvements for this project, including adding support for multiple types of accounts. We started with this because it is still one of the most popular Java projects for beginners.