Holacracy meeting bingo: Create a Holacracy variation of https://en.wikipedia.org/wiki/Buzzword_bingo to make learning the Holacracy language more fun.
Cross-talk bell: Basic version: facilitator rings a bell when someone cross-talks and they count. Who had the least cross-talks wins.
Advanced version rumored to be in use at Zappos: Have an internal currency called Zollar that people can spend on fun stuff. When the bell indicated one cross-talked that person puts a Zollar in front of them. At the end of the meeting the person with the least cross-talk gets all the Zollars.