Following articles (on this website) list various Open Source resources for IoT and M2M:
Note: some resources are not so easy to classify. Let's take the example of one that would provide a code development tool, some runtime libraries and an instanciated platform on the Internet. Where to classify it? Well, as my aim is not to provide a real taxonomy, the category/categories where I would put such a resource would mostly depend on my mood at that time .
To be continued...