Slic3r is mainly a toolpath generator for 3D printers that can read 3D models (STL, OBJ, AMF, 3MF) and convert them into G-code instructions for 3D printers.
Blender is a free and Open Source 3D animation suite that supports the entirety of the 3D pipeline—modeling, rigging, animation, simulation, rendering, compositing, motion tracking, even video editing, and game creation.