BT Indigo includes multiple packages licensed under GPLv2-like licenses. In order to comply with the obligations under those licenses, BT releases details of the packages used, and the changes we have made to those packages. Where appropriate we try to upstream these changes to the respective packages.
The structure of the releases are patchsets associated with the packages. These can be applied to the generic release version listed for each release of Indigo. The packages, version and location of the original source is included in opensource.md
Indigo supports multiple platforms, and the patchsets are separated by platform, even though many packages are common across all platforms
Enjoy
The BT Indigo Team