I have also been looking for a sync alternative to Goodsync and tested Duplicati. I found out that Duplicati only serves as a backup tool, it doesn't create normal accessible files in the destination location. In the FAQ on the Duplicati-site they confirm this:
Q: Can Duplicati store plain files instead of inside compressed folders?
A: No. Duplicati is a backup tool, not a file sync tool. If you simply sync your files, you need to be certain that the system that you are storing the files on can handle the same as your local files. For example you cannot store data from a case-sensitive filesystem on a server with a case-insensitive file system.
You also need a server-side handler that can update the remote files, otherwise you need to transfer complete files every time something changes. Duplicati is designed so it does not require any code installed on the remote machine.
If you store plain files on the server, you loose confidentiality as all filenames and file sizes are readable.
However, if this is what you want, you can search for "file mirror tool" or "file sync tool". Some open source projects that look interesting: Rclone, SparkleShare, Mirall, OwnCloud, cSync, S3 File Sync. There are many commercial solutions as well.