Inkscape -- A powerful, free design tool

• Also check out the notes on gimp

What is it?

Wikipedia

Inkscape is a free and open-source vector graphics editor; it can be used to create or edit vector graphics such as illustrations, diagrams, line arts, charts, logos and complex paintings. Inkscape's primary vector graphics format is Scalable Vector Graphics (SVG), however many other formats can be imported and exported.

Inkscape - what to use it for

• Create posters
• Create logos, technical drawings, block diagrams...
• Spice up the diagrams for your publication
• Work with and modify existing postscript or pdf files

Get it, docs, manuals

• linux distributions like Ubuntu ship it as a package (get it via apt-get)
• check out the inkscape website for documentation