Visualizing Elliptic Curves
Most visualizations of elliptic curves neglect either their complex points or their usual algebraic embedding in projective space. See the results of some other visualizations here: Link.
Projective Viewer VR
Displays real algebraic projective surfaces in RP^3 at room scale.
Looking at the Clebsch surface.
We can think of U-substitution visually as consisting of a horizontal stretch, which screws up areas, then a vertical stretch to compensate. Here's a tool to see that: Link.
This one illustrates a couple of quotient groups of Z/2 x Z/2 x Z/2 x Z/2. Press 1,2,3,4 to add the standard basis elements. Press i,u to move forward and backwards in the process of quotienting by a certain subgroup I, and j,q to do the same for another subgroup J. Link.
Shift similarity of primes mod m
Not sure how to explain this: Link
Projective Curve Viewer
Displays algebraic curves in the real projective plane. Available under the terms of the GPL. I occasionally screw up the dependencies, so if the program fails to run due to missing DLLs, let me know.