What I really do not like about posters is that they are rarely reuse-friendly, e.g. because they were created using non-open software and finally shared only on paper or as a PDF or in non-open formats or under non-open licenses.
Even for LaTeX templates, non-open licenses (usually with an -NC clause) seem to be prevailing. So I'd like to use this thread to create a list of openly licensed and easily forkable posters.