(Top Pick): This is widely considered the best PlanetCNC alternative. It is completely free and open-source. It runs on Linux (natively) and can drive milling machines, lathes, 3D printers, and robots. While it has a steeper learning curve than Windows software, it is incredibly stable and used in professional shops.

If you buy an authentic, original PlanetCNC controller (like the Mk3/4), check if it comes bundled with a license or a discount code for the TNG software software activation.