[wastholm]

KDE -- I guess they want us to call it Plasma nowadays -- still has this feature (it's off by default, but you can enable it in Desktop Effects). It's pretty clunky to use, though: you have to hold down both Shift and Meta while drawing with the mouse. And I don't think you can draw with fire.

[gerdesj]

Sadly, no fire but you can change the colour and thickness of the line. You can also set your own key bindings.