GraphTerm is a browser-based graphical terminal interface, that aims to seamlessly blend the command line and graphical user interfaces. The goal is to provide a fully backwards-compatible terminal emulator for xterm. You should be able to use it just like a regular terminal interface, accessing additional graphical features only as needed. GraphTerm builds upon two earlier projects, XMLTerm which implemented a terminal using the Mozilla framework and AjaxTerm which is an AJAX/Python terminal implementation. (Another recent project along these lines is TermKit.)
GraphTerm can be used as a collaborative graphical terminal, as a detachable terminal multiplexer (like GNU screen or tmux), or as an inline data visualization tool (sort of like the Mathematica or iPython Notebook interface, but at the shell level). You can even invoke web sites like the Online Python Tutor from the command line within GraphTerm. With tappable links, the interface is designed to be touch-friendly for use with tablets. Here is a sample screenshot illustrating graphical gls and cat command output using a 3D perspective theme (captured on OS X Lion, using Google Chrome).