Gather
This is a spreadsheet everyone can edit online. Feel free to enter your in-game name under Team 1 or Team 2. As this just puts you to a list, it might be smart to enter a timestamp next to your name so people know when you signed up.
Most cells in the sheet is editable, use this to your advantage and "chat" from it. Other then that when more people are using it a box to chat in will appear on the top right menu. You can press this to open a chat-box for instant messages.
This service is not very good on phones, but if you have downloaded the google spreadsheets app on your phone, you can access the sheet from this link:
https://docs.google.com/spreadsheets/d/1jaMTSsV8xi9tVK4BzckFAL27Z9r3dbNmVaPcoqubRe4/edit?usp=sharing
This for easier access while you're in-game or on the go.
As allways, if you have feedback, let me know!