I will use this thread to announce times in which I will do some server maintenance. So far, I’ve been doing maintenance unannounced, since the activity level here wasn’t high enough to make short down times really disruptive. Anyway, such down times usually last 10-30 minutes and not much more. So, if the forum is down for you, try it half an hour later again.
Some tasks like installing additional plugins for the forum require rebuilding the Discourse software, which seems to take about 10-20 minutes. Additionally, some maintenance activities require the virtual server this forum is running on to be halted temporarily, which of course makes this forum unavailable.
Today I’m doing a complete backup of the server and install a tag plugin, which I hope will improve the forum significantly. These tasks should be completed at about 4:00 PM GMT+1. Until then, it would be a prudent precaution to make local copies of your posts, if you decide to try write something before that time. You might not need that though, because Discourse handles caching rather well, but better be safe than sorry. 
Edit: These tasks have been completed now. You can now use tags for the topics you create. Have fun. 
Edit addendum: You need to have user level 3 to create new tags. Normal users can only select tags that have already been created by admins or level 3 users. Since there are no tags, yet, normal users will have to wait for this plugin to be usable for them.