qtFM – Lightweight file manager
lightweight, pure Qt, no kde libraries or other dependencies
full theme and mime filetype icon integration
tree, bookmarks, list, icon, detail and thumbnail views
customizable interface, rearrange views and toolbars to suit
powerful custom command system for user defined actions
customizable key bindings for built-in and custom actions
drag & drop functionality
Install qtfm in ubuntu
Download qtfm deb package from here. once you have deb package double click on it to install.
Is it lighter, than spaceFM?