I haven't installed it yet but I believe that it's more than just a reskin.

There's a custom set of desktop apps built using a their own language, Vala.

They also have a pay what you want app store to support and all apps there are FOSS.

https://developer.elementary.io/

They didn't create Vala, rather they adopted it because it's modern syntax makes it easier to write gtk+ based applications than doing it in C.

Aha thanks, that's interesting. I guess that leaves their tuning and custom apps in there then.