Magics is described as 'rapid prototyping software enables you to import a wide variety of CAD formats and to export STL files ready for rapid prototyping, tooling and manufacturing' and is an app in the photos & graphics category. There are more than 10 alternatives to Magics for a variety of platforms, including Windows, Linux, Mac, Android and iPhone. The best alternative is F3D, which is both free and Open Source. Other great apps like Magics are Netfabb, Free View Expert, Viewshape and Tatlin.
Magics is mainly a 3D Modeler but alternatives to it may also be 3D Painting Apps. Filter by these if you want a narrower list of alternatives or looking for a specific functionality of Magics.
Netfabb is not just a viewer, it provides mesh edit, repair and analysis capabilities to everyone already being or aspiring to become part of this fantastic, growing, creative, high-tech industry called Additive Manufacturing, Rapid Prototyping or 3D Printing.
The STL Viewer is FREE software for visualisation of STL or OBJ meshes created in packages such as 3D Studio Max, MAYA and Z Brush, modeled in CAD systems or generated from 3D digitalization of physical objects.