Indeed, Sailfish OS is unfortunately not totally open-source. Most closed part are the UI, like the compositor (lipstick) the homescreen UI (lipstick-jolla-home), QML components (silica) and other apps still closed-source. Last weeks, Jolla started to open-source more and more components like the weather app, all components related to Netxcloud. Check their repository for more open-source components. I’m not sure there is a complete list of closed sourced components. Ther
For further information, I invite you to watch this presentation of Jolla by @abranson a Jolla employee: https://www.youtube.com/watch?v=OSNtmT_ITvc
The event was at the hackerspace FIXME in Lausanne, Switzerland.