(Reload if the sharks die out :-D )
An implementation on A.K. Dewdneys's Wa-Tor from Scientific American's "Computer Recreations" column (reprinted in "The Armchair Universe") Blue dots are fish, large black dots are the sharks that eat them, following very simple rules.
In college, I was taken by Warren Kovach's version for Windows, in particular its phase-diagram of the population of fish against sharks (kind of living out the Lotka–Volterra equations I've recently found out.) The graph always stuck with me- even since then I haven't seen many time-based displays where time wasn't simply the X-axis, but rather the twisty line itself.
P5.js Source available (Actually just hit View Source - everything is embedded in the page.) It can act an example of two P5 apps communicating.