The Swedish Media Database (SMDB) <http://smdb.kb.se/english/> is a service of the National Library of Sweden. It is of interest to MusicBrainz mainly because the database contains a vast collection of data on records (as in audio recordings) published in Sweden. This includes older records, records which are hard to find information on, and records which have data that is hard to enter in MusicBrainz. The data can be considered very reliable as it is compiled by the National Library of Sweden. Thus it it a perfect regional database for Sweden.
Data entries may contain multiple media, and should be linked to release groups in MB.
Example of entry mentioning both CD and cassette recording:
Tintin i Kongo / No MB entry
Not previously discussed as far as I know.