This template is used on User: pages to list other projects on which the same user is active. Usage is the same as w:template:sister. Do not use this on articles as wikipedia: and commons: links in the sidebar for the same-city Wikipedia article or Commons category are handled automatically via Wikidata.
This website uses the Wikivoyage API to get and display all the information you see. This is the MediaWiki API, which is a general API for accessing data from Wikimedia projects. You can find information about it here: MediaWiki API.