Guest users can be granted the same board-level permissions as Board Members. This means they can perform similar actions such as adding tasks, completing tasks or commenting on tasks and discussions.
Guest users cannot be granted the following permissions
Custom Field Manager
Create Boards + Templates
Automation Manager (Global)
They cannot be added to teams.
Board Level Permissions
Guest users also cannot
Be a member of more than 3 boards at one time
Share the same email domain as the Rindle owner
Learn more about Adding Users
Learn more about Global User Permissions