Currently, all of Docear’s online services are down, including the recommender system. This means, you cannot register, log-in to download backups, or receive recommendations. As we have no time right now for the development of Docear, we are afraid that we won’t be able to fix this problem anytime soon. However, we adjusted the current version of Docear (v1.2) to dynamically deal with this situation. This means, as long as the services are down, the recommendation button is not shown and the registration dialog is not shown when installing Docear for the first time. As soon as the services are up again, all the buttons etc. are automatically shown again.
Update 2017-08-24: Please note that for the foreseeable future we will not continue the development of Docear as we have not enough funding and time.