If you're working on 3D designs and use a Mac, you might be looking for a free STL viewer to help you visualize and inspect your models before 3D printing. Luckily, there are several great options available for Mac users that won't cost you a penny. Here are some of the best free STL viewers for Mac:

1. MeshLab: MeshLab is a powerful open-source tool for processing and editing 3D triangular meshes. It supports a wide range of 3D file formats, including STL, and offers advanced features for visualization and analysis.

2. FreeCAD: While primarily a parametric 3D CAD modeler, FreeCAD also includes a built-in STL file viewer. It's a versatile tool that allows you to view, modify, and export STL files, making it a great choice for Mac users working with 3D printing.

3. Cura: Cura is a popular slicing software for 3D printers, but it also includes a built-in STL viewer. While its main focus is on preparing 3D models for printing, the integrated viewer can be useful for inspecting your designs before sending them to the printer.

4. 3D-Tool Free Viewer: This free viewer is designed specifically for 3D files, including STL, STEP, and IGES formats. It offers an intuitive interface and a range of visualization tools, making it a great option for Mac users working with 3D models.

5. eDrawings Viewer: Developed by SOLIDWORKS, eDrawings Viewer is a versatile tool for viewing and sharing 3D models, including STL files. While it's not as feature-rich as some other options, it's easy to use and provides a simple way to inspect STL files on your Mac.

No matter which free STL viewer you choose for your Mac, you can rest assured that you'll be able to visualize and inspect your 3D designs without breaking the bank. These tools offer a range of features and capabilities, allowing you to ensure that your models are ready for 3D printing. Try out a few of these options to find the one that best fits your workflow and needs. Happy designing and happy printing!