There is a custom on Purim to use a grager to make noise at the Megillah reading. The reason for this is the following: On Chanukah we play with a dreidel which is spun on the top because the salvation came only from Hashem who saved us from the Greeks and who did a miracle for us regarding the jug of oil. On Purim, however, we fasted and contributed to the miracle. Therefore, we turn the grager from the bottom to symbolize this.
Others say the reason why the dreidel is spun on Chanukah is because our enemies wanted to destroy our neshomah which comes from above, and on Purim our enemies wanted to kill us (our bodies), so we turn the grager from the bottom.
Why is it that the dreidel is spun on a table and the grager is spun in the air? We waged war on Chanukah on this physical plane, so we spin a dreidel on the table which is on land. However, on Purim there was no war, as we simply asked Hashem to help us. Therefore, we spin the grager in the air.
