Free actions don't take any time at all, though there may be limits to the number of free actions you can
perform in a turn. Free actions rarely incur
attacks of opportunity. Some common free actions are described below.
Dropping an item in your space or into an adjacent square is a free action.
Dropping to a prone position in your space is a free action.
In general, speaking is a free action that you can
perform even when it isn't your turn. Speaking more than few sentences is generally beyond the limit of a free action.
You can stop concentrating on an active spell as a free action.