• Gimp: The Photohop substitute. Very good at editing photographs and adding special effects to them. Don’t be afraid because of its floating toolbars. Probably you are not used to having a program divided into several independent windows, but with a little time you’ll find it an efficient way of work
• Inkscape: Nice vectorial graphics editor. What is a vectorial graphic? We could define it as a picture compound of lines, letters, polygons and symbols. Maybe not very clear? Then I recommend you to have a look to these examples. I would recommend to use Inkscape when you need to create diagrams or schematic pictures. Even, I would recommend it when you need to add circles/polygons, arrows, and text to a photograph, instead of Gimp.
• Dia: Another vectorial editor, but focused on creating diagrams. If you know Microsoft Visio, you know what I am talking about. You can do flow charts, UML diagrams, network diagrams…
• Scribus: It is one of the last programs I’ve discovered, and I’m very glad of its capabilities. You can think about it as a designing and creating document layouts software. So, you could use it to create brochures, posters, advertisings… and getting a pdf file that you can give to a professional printer company if you need it. I have even seen some pages of a catalog of a famous car manufacturer made with Scribus!
• Python + Matplotlib: Say goodbye to Matlab. Or M$ Excel, if you use it to create 2D plots… (are you sure you want to use Excel to do this graphics? O_o I hate it, and how awful it is!). Just take a look at these examples and be charmed!

As an example of all these programs, I’ll show you a poster (high res pdf – low res gziped png) I did for a student poster competiton of a scientific conferences. I’m proud of the result, not just because I did it entirely with open source software, but because I won the 3rd prize with it! *^_^*

The main layout was done, as I said, with Scribus. Managing the several text boxes was very easy with the help of styles (always use styles to define properties of text and lines in Scribus!). The diagram in the Introduction section was done with Inkscape. The schematic picture of a sample application too. The photos where enhanced with the Gimp, to get a better contrast or vivid colours. Dia was useful to get the “schematic of the developed system” in just a few minutes. And finally, the plots of the Testing and results section where draw using Python + Matplotlib. The two plots of the right were done with Matlab, because they were done by a colleague of mine (but I am converting her to the true religion :) ).

I hope that this post could be useful to all of us who need to draw anything, from personal to professional works. Good luck, and have fun with your drawings!