This open source Cycloidal Gear Builder is an evolution of a desktop app that I developed in 2012. The new version runs in modern browsers with WebGL support (if in doubt, use Chrome). The output format has changed from SVG to DXF which is more commonly used in CAD and CAM applications. If SVG output is desired the DXF output can easily be imported into the open source SVG editor Inkscape. For additional details and comments see my associated blog post.
Specify desired values in the parameters box and then click on the 'Update' button. Dependent on the specified resolution the rendering might take some time. Once done, the result can be saved as a DXF file by clicking the 'Generate DXF' button underneath the graphics window.
Use the mouse scroll wheel or the slider underneath the window to zoom in and out. Press the left mouse button and move the mouse to pan.