The mechanism of rsync + hardlinks is similar to BackupPC[1][2], which is an 18 year old open source backup tool, written in Perl, with a web UI. It supports backing up Mac, Windows, and Unix-like OSs, and is primarily for centrally backing up multiple computers. BackupPC's UI is obviously not as slick as this, but it does allow restoring individual files from a given date. If I remember correctly from 10+ year ago, their tar over SSH transport option performed better than rsync when used on a fast network.