Plesk Control Panel
Plesk Onyx faq:
https://docs.plesk.com/en-US/onyx/faq/
Plesk release notes for Onyx:
https://docs.plesk.com/release-notes/onyx/change-log/
Plesk Application Vault is the list of applications owners of websites can easily install:
https://docs.plesk.com/en-US/onyx/administrator-guide/server-administration/web-applications/application-vault/troubleshooting-app-installations.68933/#adding-your-apps-to-plesk
Plesk recently changed their catalog of available apps for installation on a website account to their own catalog. Their own catalog (May, 2019) has a lot less choices than the previous catalog.
Application is no longer available in Plesk applications catalog
https://support.plesk.com/hc/en-us/articles/360011761733-Application-is-no-longer-available-in-Plesk-applications-catalog
One of the catalogs:
http://apscatalog.com/all-app/
Google queries
dokuwiki disappeared from plesk applications
plesk available applications