Automata by Example – build cellular automata just by clicking around
demos.samgentle.com
demos.samgentle.com
If it helps, the slider down the bottom controls the speed. Or here are a few patterns that are certified non-flashy:
Expanding squares: https://demos.samgentle.com/automata-by-example/?1=1a&26=10&...
Diamond: https://demos.samgentle.com/automata-by-example/?2=10&49=10&...
Rule 30: https://demos.samgentle.com/automata-by-example/?1=10&2=10&4...
This could definitely trigger some of the epileptics I've known.
EDIT: I just noticed its when I pass through a rule I already had while drawing, it doesn't reset the grey after the rule has been changed