CURA

According to the Ulimaker website:

Ultimaker Cura is a 3D printer software that creates a seamless integration between your 3D printer, software and materials to achieve perfect prints every time.

Cross-platform, open source software, available completely free of charge
Print right away using recommended mode, or use custom mode to configure over 300 settings, for maximum control
Expert-configured and road-tested profiles make hardware and material configuration simple and fast, and achieves reliable, professional results
Out-of-the-box support for STL, OBJ, X3D, and 3MF file formats
Add even more functionality with plugins for CAD software and optimized profiles for third-party materials
Combine with Cura Connect to manage one or more network-enabled Ultimaker printers from a single interface