Zendesk is the more common of the two in our index: it runs on 4,325 websites against 37 for Docusaurus, and 2 sites use both. Counts come from real scans, not vendor claims.
Docusaurus is a tool for teams to publish documentation websites.
Zendesk is a cloud-based help desk management solution offering customizable tools to build customer service portal, knowledge base and online communities.
2 sites run both Docusaurus and Zendesk. That is 5% of the sites using Docusaurus, the smaller of the two.
Want to know which one a particular site uses? Look it up and see its whole stack, or compare two sites side by side.