Look at the Wikipedia page, it's a mix of open source and proprietary copmonents. The OS project describes itself on https://sailfishos.org/info/ as "open source based" rather than "open source". It seems they have opened up some stuff since the last time I looked, but as far as I can tell the Silica UI is still proprietary. See for example https://forum.sailfishos.org/t/silica-components-license-and...