I have a client who is currently using a free file synchronization utility on three devices which sync back to a basic file server when on the local network at his office. This is a less than adequate system that he's been using for years and just dealing with the issues. His main gripe is, that since its manual, he deletes items from sync'd folders intentionally, and depending on the timing of the other users synchronization, the items get put back into the master folder. He's not interested in cloud options due to the sensitive nature of the files, but would like similar functionality to dropbox/google drive etc with an in-house NAS unit. Can anyone recommend a software solution or other method capable of fulfilling this specific need? I.e. if one particular user removes files from a particular folder, then those files will not be replaced when other users sync up. However, they need to be able to operate independently on their own version of these files, so a constant sync between all devices isn't optimal either.