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Depending on the type of game, you can use stuff like a leverless arcade controller, such as the Flatbox or Frame1. Works well for fighting games, platformers, simpler 2D stuff. Anything that doesn't need two analog sticks or expect a mouse. Similar benefits to a keyboard, but less stuff in the way and can potentially have a more ergonomic layout. Games that need more inputs could benefit from custom controllers made for them. I heard a guy in passing talk about building a custom controller for American Truck Simulator.

The DIY controller scene is pretty healthy right now thanks to the RP2040, 3D printing, and certain firmware projects like GP2040-CE that have already done a lot of the work.