Q4OS is a Debian-based desktop Linux distribution designed to offer a classic-style user interface that is lightweight efficient (Trinity desktop) and simple tools, as well as to serve stable APIs for complex third-party applications, such as top notch web browsers, virtualization and development tools. The system is also very useful for virtual cloud environments due to its very low hardware requirements. E.g. the Trinity desktop (this torrent) minimal requirements are 300MHz CPU / 128MB RAM / 3GB disk. Note that it can mimics most of Windows XP, 7 or 10 interface in two clics.
Note from the torrent uploader: Q4OS Trinity Desktop brilliantly runs the latest software on a ten years old Atom netbook. Call that lightweight :D