Together with javascripts for tracking GUI events and scripting of the new HTML 5 elements, you get a lot of what Flash offers.
HTML 5 has a number of new elements. One of them is called Canvas. With it you can draw anything you want on screen, within its bounds. You use javascript to draw on it and you can catch any mouseclicks and similar with javascript too. If you are used to GUI toolkits on the desktop like Tk, GTK, you can liken these new elements to some of the widgets of those GUI toolkits.
Take a look at thejit to see an example of graphs in HTML 5
