So after much debate the Thunderbird Planing Group has decided on new code names for Thunderbird developmental builds/channels:

• Daily (formerly known as Shredder or Nightly)
• Earlybird (equivalent to the Aurora channel/builds for Firefox).
• Beta
• Release

Along with this new naming scheme comes the release of Thunderbird 6 to the Earlybird Channel. While the build itself seems to functioning fine, there are a couple branding issues that need to be fixed:

What is it?

• On first run it opens a new tab: Welcome to Shredder! Two problems with this, first off the Shredder name has been replaced with Daily and this an Earlybird build as well.
• Going to Help >About Earlybird brings up the About Miramar (Miramar is Thunderbird 5) background. At least it does reflect the correct build number (6.0a2) and channel name (Earlybird).

So looks like there are still a couple kinks that need to be worked out with the branding, but otherwise it appears to be functioning normally. Not sure what new features are going to be included with this release.