I have a small game which requires 4 Keys: 2 Keys to move the Player to the left/right, 1 Key to accelerate horzontal movement (dash key), and 1 Key to move vertically faster.
You can find the current project at https://github.com/jonlit/spacestarprocessing (The game idea was from my teacher, he put a task in a class test where we should complete UML diagrams and some code for the classes). I'm trying to rewrite it as a TUI game. I found that on Windows there is GetKeyState(), but I haven't found anything similar for Linux.