Nautilus!

Double Commander is a cross platform open source file manager with two panels side by side. It is inspired by Total Commander and features some new ideas.

GNU Midnight Commander is a visual file manager, licensed under GNU General Public License and therefore qualifies as Free Software. Its a feature rich full-screen text mode application that allows you to copy, move and delete files and whole directory trees, search for files and run commands in the subshell. Internal viewer and editor are included.

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. Thunar is fast and responsive with a good start up time and directory load time. Thunar is accessible using Assistive Technologies and is fully standards compliant.

Far Manager is a program for managing files and archives in Windows operating systems. Far Manager works in text mode and provides a simple and intuitive interface for performing most of the necessary actions:

"Dual pane file manager and SFTP/FTP client for Mac OS XForkLift is designed to be the fastest, most powerful file manager for the Mac. Connect to FTP or SFTP servers, manage your Amazon S3 account or your mobile devices over Bluetooth. All these features are beautifully integrated into a sophisticated, yet easy to use Cocoa based interface. Dual-pane view will dramatically increase your productivity along with state-of-the-art features like live preview, spring loaded folders and any-to-any workflow. All this to be topped by tabs, to keep your workspace nice and clean." »

An extremely fast and lightweight file manager which features tabbed browsing and user-friendly interface.

SpaceFM is a multi-panel tabbed file and desktop manager for Linux with built-in VFS, udev- or HAL-based device manager, customisable menu system, and bash integration. SpaceFM aims to provide a stable, capable file manager with significant customisation capabilities.

The simple, powerful, and sexy file manager from elementary OS.

Fast, light, and flexible file manager. Xfe only requires the FOX library to be fully functional. Plus, it can be launched from the command line in a fraction of second. Xfe can also efficiently complete terminal commands.