Lightning brings the Sunbird calendar to the popular email client, Mozilla Thunderbird and the SeaMonkey internet application suite. Lightning is a calendar extension for Mozilla Thunderbird. It offers calendaring features directly in the Thunderbird User Interface. Further integration features, such as e-mail invites or address book integration are planned for future releases.
Sunbird is a cross-platform calendar application, built upon Mozilla Toolkit. Sunbird is a full-featured and easy to use calendar application that you can use around the world.