Q-Dir is not available for Linux but there are plenty of alternatives that runs on Linux with similar functionality. The best Linux alternative is Double Commander, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 50 alternatives to Q-Dir and many of them are available for Linux so hopefully you can find a suitable replacement. Other interesting Linux alternatives to Q-Dir are Midnight Commander (Free, Open Source), Dolphin File Manager (Free, Open Source), Thunar (Free, Open Source) and fman (Freemium).
Dolphin is a file manager for KDE focusing on usability. Has three view modes: Icon, Detail and it used to have Column View like in Finder (it is not available in current version due to problems with maintaibility). Supports FTP, SCP and other protocols. Highly configurable.
Thunar is a new modern file manager for the Xfce Desktop Environment. Thunar has been designed from the ground up to be fast and easy-to-use. Its user interface is clean and intuitive, and does not include any confusing or useless options.
JumpFm is a minimalistic dual panel file manager (currently released only for Windows, Mac, and Linux) that lets you navigate your file system very efficiently. Mac releases can be found at https://github.