I had the demo setup 5.9 of Activiti running and I can contact the activiti-explorer but not the url you were shown here.
-Is that no longer possible in the 5.9 version? -If not, is there another way to see the features of the REST-API? I'm not sure if the user-guide is up to date for the REST-API. Is it? Because I sometimes read here that different people would contribute new rest features. Are there now more features then shown in the userguide?
This is not possible in Activiti 5.9. You can view all the rest services in the user guide. In the meantime we're working on Activiti 5.10 and that may have additional REST services. But for that, the source code is the only place to now which are available.