The Minskytron is a visual synthesizer based on 3 interconnected oscillators much like a Moog synthesizer. Each oscillator advances an x- and a y-coordinate over an elliptical function, plotting a dot at the given position at each frame. site 
The formula is based on the ancient art of drawing a circle using additions/subtractions and bitwise right-shifts.
x := x – (y >> 4) y := y + (x >> 4) plot repeat
The javascript implementation is based on emulation code by Barry Silverman, Brian Silverman, and Vadim Gerasimov. The emulator was originally written for running Spacewar, the earliest known digital video game. site
The original code was extended to support some additional instructions and auxiliary hardware. Moreover, the shift/rotate instructions and the arithmetics were rewritten (include an emulation of the hardware multiply/divide option), and cycle counts were added for accurate timing and frame rates. Some importance was put in the recreation of the appearance of the original CRT display and the unique experience conveyed by it.
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Errors accumulate and eventually create overflows which introduce a pseudo-random effects. I am reminded of the Imlac program Kaleidoscope. We spent hours studying the range of behavior of this very simple program.
See Imlac PDS-1