Inkscape is an open source 2D vector graphic program. It roughly positions itself in the same software type as CorelDraw, Freehand and Adobe Illustrator. Unlike Photoshop or Gimp, Inkscape stores its graphics in a vector format. What this imply is that drawings created with Inkscape are not dependent on pixel-resolution.
To my knowledge, Inkscape can be a viable alternative to the commercial illustration programs. However, it did not seem to have gained popularity in this area. Notwithstanding this, Inkscape should be pretty fine as a program for creating 2D product design visuals.