A lot of SL residents send notecards when message delivery is important or the message is quite long. It is kind of SL e-mail. SpeedLight makes managing such notecards easier.
The notecard can be composed and sent directly from an IM dialog with a specific person:
The copy of the sent notecard stays in your inventory.
Any notecard you receive while being logged in with SpeedLight also appears in IM dialog:
You can accept the notecard and view it, or discard (but notecard is still available in inventory).
You can also quickly reply to notecard with another notecard!