Fedora is considerably upstream for all three. I expect the efforts are mainly repackaging, so instead of repacking RHEL into SL, they'll aid in the repackaging of RHEL into CentOS.

Fedora Scientific Spin is produced by the Fedora Project's Science and Technology special interest group (SIG). It's based on KDE.

https://labs.fedoraproject.org/en/scientific/ https://fedoraproject.org/wiki/Category:SciTech_SIG?rd=SIGs/...

I don't think there's any relationship between this SIG and Scientific Linux.