If you need to set up a meeting, and keep track of who's attending and who is not, Lightning can do this as well as allow you to send invitations to people who do not have Thunderbird/Lightning, including Microsoft Outlook users!
Creating the Event
Create a new event in Lightning, by either going to "File, New, Event" or clicking on the "New Event" button on the toolbar if it is immediately accessible.
Click on the "Invite Attendees" button.
The screen that pops up is shown below:
On the left next to the yellow person icon, you add attendees from your address book.
After adding all the attendees that you would like to attend the meeting, hit OK.
Be sure to check the "Notify attendees" box if it is not already checked.