Trackball mice used to be fairly common, but most people these days choose to use trackpads or conventional mice. Despite that, trackballs often a number of advantages over other mice — particularly for people who spend a lot of time on their computers. You can spin the trackball with your fingers instead of moving your entire hand, which can help reduce repetitive stress injuries to your wrist. Trackballs can also help you more accurately move your cursor. If a trackball sounds appealing to you, there is an open source design called Ploopy that you can 3D print yourself.
There are trackballs on the market, but there are currently only a couple of models available and so your options are limited. I’ve personally owned many Logitech M570 Trackball mice, because they’re very comfortable. But they’re also wireless, and always end up failing eventually. I’m currently using a Kensington Orbit Trackball, but it features a scroll ring and has no center click. You get the idea—everything on the market has a downside. With Ploopy, you can customize the design to fit your unique preferences.
You can purchase Ploopy as a kit, or use the provided design files to make your own. The model files for 3D printing, the required code, and the custom PCB files are all available on GitHub. Ploopy uses two PCBs that are soldered together at a 90 degree angle. The standard Ploopy layout positions the trackball underneath your index finger. If you prefer a different layout, such as with the trackball under your thumb, then you’ll need to redesign both PCBs and the 3D models. But that’s the beauty of open source projects like this, because you can alter the design however you like.