sudo apt-get install dolphin

Nautilus | Homepage
The default file manager in GNOME, Nautilus has an intuitive interface and offers features like previews, sorting, three view modes (icons, list, compact), bookmarks. Nautilus can be expanded via plugins and it also supports context menus.

sudo apt-get install nautilus

Konqueror | Homepage
Konqueror is a powerful KDE application which has been around for years. It is not only a file manager, but a web browser or image viewer too, and more. I will highlight here the main features that are brought by Konqueror as a file manager only: profiles, extensions, fullscreen mode, window splitting left/right or top/bottom, four view modes (icons, details, columns, terminal emulator), previews or sorting.

sudo apt-get install konqueror

PCManFM | Homepage
PCManFM is a fast and lightweight GTK file manager with features like tabs, file/folder sorting, four view modes (icon view, thumbnail view, compact view and detailed list view), File-Roller archiver integration, bookmarks.

sudo apt-get install pcmanfm

Thunar | Homepage
Written in GTK, this is the default file manager in the Xfce desktop environment, which has the goal of staying simplistic and only offering basic features. Tab support is missing, however Thunar features a left sidebar for fast access to common places, sorting, zooming, three view modes.

sudo apt-get install thunar

ROX-Filer | Homepage
ROX-Filer is yet another GTK file manager, starting by default with a compact interface, that is only a toolbar at the top and the space for displaying files and folders occupying the rest of the window.

sudo apt-get install rox-filer

Xfe | Homepage
Xfe is a great file manager written using the FOX toolkit, and although it doesn’t blend very well with neither KDE or GNOME, it has some cool features and a somewhat different way of using it, which can please certain users.

sudo apt-get install xfe

GNOME-Commander | Homepage
As its name suggests, GNOME Commander is a twin-panel file manager for GNOME, with an interface that resembles the one of Midnight Commander.

sudo apt-get install gnome-commander

Krusader | Homepage
I think this is *the* twin-panel file manager for KDE. Krusader brings any feature possible, and can be configured to behave differently depending on the user’s needs.

sudo apt-get install krusader

Midnight Commander | Homepage
Midnight Commander is a popular twin-panel file manager for the terminal, based on ncurses library and therefore using a text-user interface.

sudo apt-get install mc

Vifm | Homepage
Vifm is yet another twin-panel file manager for the console, also built using ncurses, including Vim-style keyboard shortcuts.

sudo apt-get install vifm

emelFM2 | Homepage
This is yet another GTK2-based file manager with a twin-panel interface, and comes with functions to perform basic file management functions, an output panel, run as root.

sudo apt-get install emelfm2

Dired | Homepage
Dired is the default file manager in the powerful Emacs application and it can be started pressing Ctrl+X and then pressing D. Dired has support for file operations, including creating symlinks or hard links, change permissions, encrypt/decrypt files, diff and integration with many other tools. Dired also features an embedded image viewer.

sudo apt-get install emacs # start it with ^X-D

Tux Commander | Homepage
Yet another twin-panel file manager, Tux Commander offers simple file manipulation functions, bookmarks, network support, plugins support, configuration of external applications.

sudo apt-get install tuxcmd

Double Commander | Homepage
Double Commander is not included by default in Ubuntu’s 11.04 repositories, but I included instructions on how to install it from a PPA. Double Commander offers both GTK and Qt interfaces (so the first one blends well in GNOME while I recommend the second one for KDE), comes with a twin-panel style and includes a big number of configuration options.

sudo add-apt-repository ppa:alexx2000/doublecmd
sudo apt-get update
sudo apt-get install doublecmd-gtk # for the GTK (GNOME) version
sudo apt-get install doublecmd-qt # for the Qt (KDE) interface

Gentoo | Homepage
This is not the Linux distro although it has the same name. Gentoo is another GTK two-panel file manager with functional buttons at bottom. Although Gentoo seems a pretty decent file manager and provides enough configuration options, its interface design is kind of cluttered.

sudo apt-get install gentoo

Worker | Homepage
Worker is a simple file manager which doesn’t have a top notch interface, however it has features like twin-panels and shortcut buttons to file management functions.

sudo apt-get install worker

FileRunner | Homepage
FileRunner is an older twin-panel file manager (it hasn’t been updated since 1999) written in Tcl/Tk which provides a simple yet pretty powerful interface. One of the big downsides of FileRunner is that when you click a file it will automatically try to display it. I did it by mistake with an ISO image and FileRunner rendered by computer almost completely unresponsive, so I had to kill it in the console. Although I do not believe FileRunner is fit as a 2011 file manager, some might prefer it since it’s really light on resources.

sudo apt-get install filerunner

Lfm | Homepage
Last File Manager, or Lfm for short is an ncurses file manager for the terminal which follows the model used by Midnight Commander.

sudo apt-get install lfm

muCommander | Homepage
muCommander is a typical twin-panel file manager written in Java with features like window splitting, bookmarks, sorting, quick buttons for various functions.

To install in Ubuntu, download the DEB file from here, then make sure you have Java installed and type sudo dpkg -i mucommander_0.8.5_all.deb in a terminal.