In a similar style to this. For helping students train for debating and public speaking.
Put a list of topics into a glossary and set's up the random glossary entry block. A laptop is set up at the front of the classroom so that the person at the front can see it. Students take it in turns to come up to the front, refresh the page and speak for 1 minute on that topic off the top of their head.
After the class make the glossary open for all to see and their homework is to pick another topic than the one they spoke on and write another 1 min speech for next week.