Addressing an issue whereby Sunbird can't integrate calendar and email functionality with Thunderbird, the Mozilla Foundation is working on a project called Lightning. Lightning 0.1, is planned for release in November and will ultimately provide better Thunderbird integration, including linking emails and tasks.
The roadmap outlines some of the features that will be included in the first two versions of Lightning and in future releases of the project. Lightning 0.1, which is planned for release in November, will include fixes for the most important bugs, such as those that cause the loss of data. The team also hopes to be able to use the software as their working calendar application by this stage, a process known as 'dogfooding'. This relies on Lightning being able to do calendar sharing using the WebDAV protocol.