A Motivator is a role that can target a player at Night to allow them to use an extra action during the following Night. Note that factional abilities such as the Mafia's Night-kill cannot be used twice in one Night.
Generally speaking, Motivators are Town-aligned, but not seen outside role madness games.
Some moderators will have their version of Motivator allow a player to use an extra action during the Night they are targeted. This is not so easy to resolve in a streamlined manner, though - the moderator has to wait for the Night action submission deadline, and then allow the Motivated player to send in another action.
A Direct Motivator is a variant of this role that gets around the timing issues by having the Direct Motivator (rather than their target) choose the target for the second action themself. In this case, the Direct Motivator's target might well be unaware that their action had been copied (in much the same way that a player who is roleblocked would typically be unaware of the fact that their action had been blocked).
Use and Power
Motivator is a swingy way to increase its faction's overall power, as there is no guarantee that it will target Town. As long as it cannot cause a role or combination to become unreasonably powerful, it's usually considered fine overall.