muCommander is a cross-platform file manager that features support for FTP, SFTP, SMB, NFS, HTTP, Bonjour/Zeroconf, email attachments, Zip/RAR/Tar/Gzip/Bzip2/ISO/NRG/AR/Deb/LST archives, universal bookmarks, credentials management, themes, multiple windows, full keyboard management, and many configuration options. It is a free and open source file management application that's well-designed.
Here are some screenshots to illustrate the features and user interface of this application:
Double Commander
Far Manager
Q-Dir
One Commander
DiskBoss