Here is something that allows one to create circular objects that can go at a specified initial velocity: https://mjduniverse.com/gravity-simulator/

Objects can have a certain color, radius, and mass. Furthermore, one can zoom in and out using the buttons on the right.

I will soon update this. Here is a todo list:

• Making the simulation faster
• Adding a button that allows one to create orbits
• Adding a button that alllows one to save the simulation.
• Allowing one to zoom in and out using the plus and minus keys and the mouse wheel.
• A preview of the object.