Slic3r

Slic3r is the tool for converting a digital 3D model into printing instructions for your 3D printer. It cuts the model into horizontal slices (layers), generates toolpaths to fill them and calculates the amount of material to be extruded. It features Print beautiful colored objects, or use your secondary extruder to build support material, reads STL, AMF and OBJ files while it can output G-code and SVG files, download, double click and enjoy, you can choose to print a thicker infill to benefit from low layer heights on perimeters and still keep your print time within a reasonable amount, and manage multiple printers, filaments and build styles.