As it seems, for about one year there has been a new Embedded Projects Journal (in German). This magazine focuses entirely on FOSS embedded projects and open hardware. The idea is to have a magazine written by the community for the community. Plus, the magazine and all its articles are freely redistributable.
It's a pity that I've only noticed about this now. Let's hope more people learn about it, now that I'm mentioning it here.
If you want to contribute, feel free to contact the journal's makers.