International Council of Onomastic Sciences (ICOS) - General information
https://icosweb.net/drupal/

International Hydrographic Organization (IHO)

• General information
  
  English: https://www.iho.int/srv1/index.php?lang=en
  French: https://www.iho.int/srv1/index.php?lang=fr
• GEBCO Gazetteer of Undersea Features and IHO Sub-Committee on Undersea Feature Names (SCUFN)
  http://www.gebco.net/data_and_products/undersea_feature_names/

International Organization for Standardization (ISO)

• General information and ISO catalogue
  http://www.iso.ch/
• ISO Technical Committee dealing with Geographic Information / Geomatics
  https://committee.iso.org/home/tc211

Organisation Africaine de Cartographie et de Télédétection (OACT) / African Organization of Cartography and Remote Sensing (AOCRS)
http://www.oact.dz/oact/

Scientific Committee on Antarctic Research (SCAR) - Gazetteer of Antarctica
https://data.aad.gov.au/aadc/gaz/scar/

Unicode Consortium
http://www.unicode.org/unicode/consortium/memblogo.html

Country names

• in the German language (StAGN)
  http://www.stagn.de/liste-staatennamen
• France - Géoportail, le portail des territoires et des citoyens
  http://www.geoportail.gouv.fr/accueil
• in the Polish language (Commission on Standardization of Geographical Names outside Poland)
  http://ksng.gugik.gov.pl/english/wykaz.php
• EuroGeoNames
  http://www.eurogeographics.org/eurogeonames

Exonyms

• in the Dutch language (with pronunciation being added)
  http://taaladvies.net/taal/aardrijkskundige-namen
• in the German language (second edition, StAGN)
  http://www.stagn.de/exonyme-deutsch

Gazetteers

• Alexandria Digital Library Project, University of California
  http://www.alexandria.ucsb.edu/

Letters and languages database

• http://www.eki.ee/letter/