At a session/open stage:
Someone starts, without stopping, other enter, some leave.
No discussions, everyone can enter, everyone should leave after some time.
On entrance one nicht bring up a thing/theme.
Variation 1: kicking jam, every enter is accompanied by a leave. Means the number of people on stage has a limit.
Variation 2: put a limit on peoples stage time, e.g. a change after 3 minutes.