This is a simple program that simulates circles and rectangles moving around.
Pretty simple to use, just click one of the buttons to select a shape, then click on the canvas (darkish gray area) to place a shape. Also, you can move the circle with WASD to see how it reacts or collides with other shapes.
This is a very simple physics sim/engine that does cut a lot of corners, but uhh yeah it simulates basic collisions. It doesnt have rotations or anything, might get slightly laggy at high object counts and doesn't have a whole lot of space for testing (the small space helps keep the performance better, since there ends up being less objects)
Just as a disclaimer, this isn't trying to be anything fancy - the point is to show that a physics engine can be made with just plain JS and HTML5, and nothing else
Thanks to @Lesbiswan on Discord (queerchaosgremlin on Github) for teaching me the circle-circle and circle-rectangle collisions, no way I would have figured them out myself