After some more server tweaks, I decided to install Nexuiz Classic, one of the best (or perhaps the best?) first-person shooter games out there. Of course there is still Xonotic and I am quite eager to install this one too. However there is not much room left for another game because we almost hit the 1 GB RAM limit. In fact without Minetest I would neither have to worry about RAM nor CPU performance but I like the challenge and the game, so it is definitely going to stay. I have recently installed the excellent homedecor modpack as well as no_guests, areas, grass, moss and ... fireworks. Well, it's almost New Year, isn't it. I was not really happy with protector and I hope areas will do a better job.
I also had to adjust the maximum player limit for Freeciv because 32 AI opponents can cause quite a lot of temporary CPU load. We are back at 16 now but I hope I can raise the limit again in the future. So far and Happy New Year.