Hi there,
SoonKhen, the former Executive Director of Rethink Charity USA here.
I can confirm that Nonlinear was previously fiscally sponsored by Rethink Charity under a Model C sponsorship. A Model C fiscal sponsorship functions more like a grantor-grantee relationship; more information about it can be found here. In Model C sponsorships, the projects fiscally sponsored by Rethink Charity were not projects of Rethink Charity itself, but rather belonged to the fiscal sponsees. Our responsibilities included accepting grants and, according to the agreement and project budget, disbursing grants to sponsees, as well as monitoring their progress through reports they submitted. The board of Rethink Charity was not the board of Nonlinear.
I did this quite a few times throughout my career, my first sabbatical was after graduating and it got me moving into higher income country for a programming career. Soon after I joined a startup that is more mission driven and altruistic. Then I took another sabbatical as the startup was winding down and as I started reading about EA. I managed to convince my previous boss at the startup about EA too. I then joined another startup to rack up more savings and had another sabbatical where I was more determined to work at a highly impactful job. Seems like every sabbatical I took I get closer to EA ideas and ultimately stumbled upon a good fit at an effective giving org. I highly recommend people to take breaks/sabbaticals to help reorient yourself.
Sorry Habryka! Can't believe I missed it. I've added the link above.