The main features in Lightning are similar to those in Sunbird, allowing you to manage several calendars at the same time.
You can add dates and appointments just by clicking on a specific date and filling in the necessary fields: name, location, date, and frequency. The calendar can be viewed in three different modes: by month, by week, or by hour.
Apart from that, Lightning installs a sidebar on Thunderbird that shows a preview of the events coming up that month, day, or in the next few days.
Supported by Thunderbird versions 1.5 and 2.0.0.