Lightning is available in 32-bit and 64-bit versions for Windows, OS X and Linux.
Version 0.9 was the last planned release for Thunderbird 2. A calendar was originally to be fully integrated into Thunderbird 3, but those plans were changed due to concerns with the product's maturity and level of support. Lightning 1.0b2 is compatible with Thunderbird 3.1, Lightning 1.0b5 is compatible with Thunderbird 5 and 6, and Lightning 1.0b7 is compatible with Thunderbird 7. Lightning 1.0 was released to the public on November 7, 2011. It was released alongside Thunderbird 8.0. Since then, every Thunderbird release has been accompanied by a compatible Lightning point release.