On MSE, many users include diagrams with their solutions to help illustrate concepts and make their solutions clearer. Is there an optimal software for doing so? Any recommendations are greatly appreciated!
Thanks in Advance!
The Geometer's Sketchpad® might be helpful. The Geometer's Sketchpad® (Software)
Here is a demonstration video Geometer's Sketchpad: Demonstration
It is targeted to grade levels 3 to 12, I suppose it would meet the need of the most users unless you want something more high-end.
You do need to purchase a license to use the complete edition. However, they do offer a demo to try out with. Trial Version
You may want to see math3d.org, the 3D analogue if Desmos. It has intuitive user interface and 3D graphing support.