It's a free software package that can create and build 3D objects. By contrast, Cura is a free 3D "slicer" program that converts digital models into layers that can be sent to a 3D printer.

When you think of slicers for FDM 3D printing — especially free slicers — you probably think of Cura, Slic3r, or PrusaSlicer. There are fans of MatterControl and many people pay for Simplify3D.