In the prebuilt UI, if you enable chat in your room, participants can chat with each other and see the participant list. Some top level bullet points:
Open chat and the participant list by clicking on Chat at the bottom of the screen while in a call
Chats are fully encrypted
Chat is text only
You can download a copy of your chat history as a text file
Click Participant list to see a list of everyone in the call
Pro tip! You can change your name via the Participant list menu
More
Close a chat by clicking the close (x) icon. Or click the chat icon again
If you have the chat pane closed, a red notification appears on the chat icon, to let you know when someone has posted a new message
Clicking on a link shared in a chat opens in a new tab