Yeh, a buddy of mine raves about Syncthing. I'm trying to build something though for the less-technical user. (Admittedly, I probably won't find less-technical users on HackerNews !)

Windows <> iOS would be a really nice feature. I'm surprised Microsoft didn't add something like that to the Link to Windows app: https://apps.apple.com/us/app/link-to-windows/id6443686328