BlueSpice, based on MediaWiki, is an open source alternative to Confluence 

Knowledge management is a key to success in modern enterprises—but it is not exactly easy to achieve. Keeping track of all relevant details across all employees is a huge challenge, especially in agile environments, which most companies say they are.

Most companies resort to buying wiki-like solutions, such as Confluence from Atlassian, which exposes them to the lock-in effect of proprietary software. But many would do well to consider BlueSpice, an open source alternative to Atlassian Confluence that has a noble ancestry: it’s based on Wikipedia’s MediaWiki.

Source: Manage knowledge with BlueSpice, an open source alternative to Confluence