Ridual is a dual-pane file manager for GNOME. It features tight integration with GNOME (providing GVFS mount support, bookmarks and user directories, a removable drives list, file icons, and application associations), keyboard-oriented control (with adjustable shortcuts for everything, single-window dialogs, and messages), and advanced tasks and queues management.
FileRunner is a two-pane file manager for Unix. It is simple and efficient and has a built-in FTP/SFTP/adb client. It does a reasonable (and improving) job on Windows systems. It features a simple and powerful interface, history and Hotlist (bookmarks), a recursive directory menu of the entire filesystem tree, browsing FTP, sFTP, and adb directories as easily as normal directories, asynchronous file transfers, cached directory listings, asynchronous file operations, built-in command shell windows synchronized with file panels, extensibility by adding your own command buttons, and user-defined file pattern/actions.