*) grid
*) multiple MetaPost pictures per file
*) circle resizing
*) font selection
*) line labels on canvas
*) more options for label placement (tangent slope, ...)
*) create MetaPost preview on the fly
*) undo/redo
*) switch to export / not export object
*) choose type of arrow (none, one, both)
*) more items (ovals, rectangles, ...)
*) export to other graph drawing packages (xfig, xypic, ...)
*) clone function to duplicate items (for example, states with loops)
...