These are free SketchUp plugins, developed by Regular Polygon, to create various 2D and 3D shapes and curves.
Ellipse This plugin creates an ellipse based on parameter values for the length and width. It has an option to draw the focus points. Superellipse This plugin creates a superellipse based on parameter values for length, width, and squareness. A superellipse is a 2D shape that varies between an ellipse and a rectangle. Superellipsoid This plugin creates a superellipsoid. A superellipsoid is a 3D shape that can vary between a sphere and a cube. Actually, the shape is more general than that. Sphere This plugin creates a sphere based on the parameter value for the radius. You can control the amount of geometry created, and there are options for the edge visibility properties. Torus This plugin creates a torus or a twisted torus based on the parameters for inner radius, outer radius, and number of twists. You can also control the amount of geometry created. Loxodrome This plugin creates a loxodrome curve based on the radius, number of windings, and directional bearing. The loxodrome is a spherical spiral, which crosses all meridians of longitude at the same angle. Spherical Spiral This plugin creates an Archimedean spherical spiral based on the radius and number of windings. It is an Archimedean spiral because the windings are all an equal distance apart. Menger Sponge This plugin is basically an exercise using the SketchUp API to create a 3D fractal. In this case, a Menger Sponge for levels 1-5. Sierpinski Tetrahedron This plugin is basically an exercise using the SketchUp API to create a 3D fractal. In this case, a Sierpinski Tetrahedron for levels 1-7.