Dominos
Dominoes were small blocks that could be arranged in such a way that when one fell over, it started a chain reaction that knocked each successive domino down.
In 2384, Dr. Erin Macdonald used falling dominoes to illustrate how one small change effected during time travel could have a larger impact. The dominoes were arranged in the shape of the Starfleet delta when viewed from overhead. (PRO: "Temporal Mechanics 101")