BookStack
Documentation & Wikis
Self-hosted wiki that organises content into books, chapters and pages.
Free self-hostedOpen source · MIT

Categories
Entries in our catalogue that can take over from Confluence. Each one states why, and links the vendor's own source for the claim.
Documentation & Wikis
Self-hosted wiki that organises content into books, chapters and pages.
Why it can replace Confluence: Vendor page is titled "BookStack: An Open Source Alternative to Confluence". Source
Documentation & Wikis
Self-hosted wiki and documentation platform with real-time collaborative editing.
Also offers paid editions — see the detail.
Why it can replace Confluence: Ships a documented Confluence importer: upload the ZIP file exported from Confluence. Source