All of these resources are free to download and use. Of the more than 350 models ... and you can also use the built-in 3D model viewer not just for STL and 3MF files but for G-Codes as well. The ...

It is another nice STL file editor that you can download from here ... which you can edit 3D models like STL. It also lets you edit video files. 3D Slash is a free online STL editor.

To use it, you can download it from freecadweb.org. MeshLab is a great free and open-source ... file formats to visualize a 3D model in it include OBJ, STL, DAE, 3DS, PLY, PTX, VMI, X3D, etc.