Various discrete simulations of 2D waves. Most break down after a long time because boundary conditions don't work that well.
If they run slowly, try shrinking the window to reduce the effort needed to simulate.

mouse - perturb background with the movement of the cursor
square - propogation of an initially square displacement becomes circular
double slit - interference between two sources
lens - converging lens focuses light
line - two oscillating source lines creates a stronger signal in the direction perpendicular to the lines
shadow - diffraction around an object creates a bright spot at the center of its shadow
dipole - oscillating dipole field
doppler - doppler effect of a moving source
shock - shock wave of object moving at constant velocity
laser - each cell is influenced by the cells around it and actively amplified, eventually reaching a resonance which forms a strengthened output (definitely doesn't work as intended rn)
gradient index - quadratic variation of index of refraction results in convergence of wavefronts to a common focal point (see EuPhO 2023/T1)
mirage - highway mirage effect mimics the reflection of light water
boom - supersonic plane flies in variable index of refraction atmosphere