A project step in Projectplace can indicate different things. It could be a go-live in an IT project or a decision where a steering group needs to make sure a number of activities are done.
Today, there is no way to add any type of checklist to a project step. I think this needs to be possible, for example by making it possible to connect cards to a project step, or connect a board to the step for that matter. It used to be possible to connect a board to a step, and see the board using the mouse over. Today, you can still connect the board to the step, but you cannot see the connection.