Welcome from me too! I have been looking up the Gigatonne challenge in November, because, of all places, I ended up at the UNDP Accelerator Labs. Gigatonne reminded me of a model dreamed up years ago, by @nadia and others, called Open&Change, which ran for a very large grant (100 mil! We got shortlisted, but eventually the funder made a different choice. It was fun anyway). The similarity between the two ideas is the idea of scale: not one big box, but many smaller ones.
As for Gigatonne itself, I saw a lot of documentation, but it seemed not up-to-date. I was probably looking in the wrong place. Maybe you could point to a link describing where you are now?
And finally,
Maybe you will enjoy this: https://witness.scifieconomicslab.net. Yudha and I are quite involved in this, so if it piques your curiosity you can ask us.