MusicBrainz database is used by many applications such as Headphones or MusizBrainz Picard. The one major issue with the database is that the official service is slow and often unavailable while mirrors are either paid or unreliable long term. The server can be installed from scratch locally but is quite tedious which is why it is easier to run the server as a virtual machine. It is not as efficient as the entire OS will have to run in the background but it much easier to setup. Virtual Box can be used to run the VM without any changes but there is no need to run multiple Virtual Machine Managers so in this case QEMU is used.