Sector Index A-Z can be used to search (as well as list) content in an alphabetical index - either by the title of a content node, or by an assigned topic.
The Sector A-Z (by Title) view is a Search API view run from a full-text Search API index. Sector A-Z (by Topic) is a Drupal content view and uses double grouping to list the topics A-Z, followed by all the nodes that are assigned to the topic.
This sample content is a node of the content type Index assigned to topic O.
The Sector Index documentation on sector.nz introduces the main features and functionality, and provides links and help for sitebuilders to customise Sector Index A-Z for their needs.