<i>you can roll your own Excel clone fairly easily</i><p>Well, it would need to be able to add rows/columns and delete them.  Copy/pastability would help, too.  A necessary pre-requisite for that is going to be the ability to select entire columns at a time -- that's going to have to be custom-done because your browser isn't that smart.  Let's see, an undo wouldn't hurt.  Oh, and the escape out of editing mode.  And resizing when you overflow a single cell.    Speaking of which, drag and drop resizing on arbitrary rows/columns.<p>There's probably a few requirements I'm missing, but no problem, I can whip up a Stack Overflow clone in like a weekend and solicit suggestions on what one or two trivial details I still need to implement to duplicate the thousands of man years in Excel.