I'm bored and kinda want project ideas

I'm bored and don't have anything else going on for a while, so I thought a good old C++ project would be fun. Problem is, I don't have any ideas. So if you have any ideas at all, please give them to me

My criteria is:

I don't want to have to use a graphics library (that doesn't mean it can't have any graphics, since terminal line interfaces are okay enough for that),

I don't want to do games,

and I want it to be big enough to be a multi month projects

Some of my previous projects were a 2000 ELO chess engine, a half decent raytracer, and a NN trained on mnist with no library.

https://redd.it/1oydjz2
@r_cpp