Please note that this site is going to be terminated. You'll be able to access the project at https://github.com/mondalaci/ultimate-commander
Ultimate Commander is a two-pane file manager developed with a special focus on usability. It's a free software and it currently runs on Linux.
Ultimate Commander was my Master's Thesis project and its development was halted in the middle of 2006. It's not feature complete, so it's not intended to be used for production, but I think user interface- and interaction-wise it has some good ideas worth exploring.