MapMaker is a multi-platform (Windows, OS X and GNU/Linux) tool to assemble several images together to create a full map, annotate it and export the resulting image to a bitmap or vector image. It's licensed under GNU GPLv3 license and is available in English (native language of the application) and in French.
You can download latest versions on : http://dev.kervala.net/projects/mapmaker/files and the full C++ source on : http://hg.kervala.net/mapmaker
It should be simple enough to understand how to use it, but you can see below the main features of MakMaker.
The main screen. You have a tool bar at the right, the different tools are :