Question: May one play with a dreidel on Shabbos?
Answer: The Shulchan Aruch (CM 370:2) writes that one mustn’t gamble or play betting games. Doing so is forbidden derabanan because it is akin to stealing as when losing, one isn’t happy about giving up their money, etc. The Mishna Berura (322:22) writes that this prohibition applies equally to playing with one’s own children even though they would be happy to share, as it will lead to playing with others. Elsewhere, (Biur Halachah 670) he writes that one shouldn’t spend one’s time on Chanuka playing such games.
Nonetheless, many have the minhag to bet with a dreidel over Chanuka (See Taamei Haminhagim 859). To avoid proper gambling, many only play with nuts and sweets rather than money.
Others justify this practice when playing with small amounts of money as people playing together with their families are particularly close and generous over Chanuka and we aren’t worried about the prohibition (See Nitei Gavriel, Chanuka 51:n5).
Nonetheless, the Rema (OC 338:5) and Mishna Berura (ibid) write that one mustn’t play such games on Shabbos, as winning and losing involves a transaction. However, one doesn’t need to stop one’s young children from playing such games (See Shemiras Shabbos Kehilchasa 16:32).As dreidels are primarily children’s toys, R’ Moshe Feinstein (Igros Moshe OC 5:22:10) writes that they aren’t muktza and they may be spun by adults on Shabbos, too.