The Preview app has markup / annotate tools like rectangle, oval, line, text, speech bubble, thought bubble. Is there a pen or pencil tool that lets you draw lines in a freehand way?
(I'm using Preview version 7.0 (826.4) in OS X Mavericks 10.9.5)
Yes, Preview in OS X 10.10 (Yosemite) has a freehand tool. Access it within Preview from the "Markup Toolbar" icon of the .JPG or .PDF file you have open.
When you click on that icon, the Markup toolbar appears, and the freehand "sketch" tool is the 3rd icon from the left, in blue in the image below.
and it offers a smoothing option as well as a freehand mode.