Recently I had to design a poster for a conference. I was thinking about which tool to use for it. One of a researcher on our lab suggested me to use a free and open source tool called Scribus. I hadn't used it before but found that it is really helpful for designing the poster.
Even though I'm not good at designing posters like stuff, I had to put a big effort to come up with my poster. Following image shows how it finally looked. It may not have been designed considering all the Do's and Dont's of designing academic posters since I hadn't enough time to worry about them.
I hope Scribus will be the tool for me to prepare posters for a long time from now on.