Seedlings is a pre-release version that is provided to the community in the months coming up to the next major release. It is young, sometimes experimental, code that has not gone through the full release QA cycle. It's primary purpose is to allow subscribers and partners or even peopole who are merely curious about what Totara is, to install a copy of the next upcoming release to evaluate the features and become familar with the code - but it is unsupported, it WILL have bugs, and the final release version WILL be different in some respects depending on partner feedback.