news://number1.nntp.dca.giganews.com/mozilla.dev.ports.os2
Lightning is a Calendar extension specifically designed for Thunderbird. It is currently under heavy development and was released in version 0.1 about a week ago.
I thought people might want to take a look, so I built it, and it's now available (as a nightly, built close in time to the official 0.1 release) from my builds page (http://weilbacher.org/Mozilla/builds.html).
It works with PmW-Tb 1.5.* and probably Thunderbird 1.5.* but probably not with TB 1.0.x. It should be mostly usable but it could also wreck your profile (BACKUP!).
Source: OS2VOICE