MediaWiki v Confluence

Comparison Chart

Attribute	MediaWiki	Confluence	Why is it important?
License	GNU GPL	proprietary	Fully free software protects your investment because it's reversible and extensible from the bottom-up. It's never tied to the fate of a sole proprietor, and not subject to vendor lock-in.
Integration	almost anything	mostly Atlassian products	MediaWiki can be, and is, integrated with a wide variety of other systems. Most importantly for the Enterprise user, a whole open authentication framework allows MediaWiki to be integrated with just about any existing authentication system. Atlassian likes to brag about how integrated Confluence is with their other systems (BitBucket, JIRA, Bamboo, FishEye, Crucible, HipChat). While it's true that these can be integrated (and work well out of the box), these extra products come at extra cost. Integrating Confluence with any product that is not sold by Atlassian is a different question.
Customization	Wiki	Confluence	discussion
Ease of Use	Wiki	Confluence	discussion
Intended Audience	Wiki	Confluence	discussion
Gartner Magic Quadrant			This is a red herring. There is no way that MediaWiki would ever be listed by Gartner since they review vendors. MediaWiki is produced by the Wikimedia Foundation (WMF), a non-profit foundation. They are not a software vendor. They'll never be listed by Gartner in any MQ unless Gartner changes their methodology. Besides, Atlassian was named in the 2017 MQ for "Enterprise Agile Planning Tools", not for wikis, not for collaboration, not for knowledge management.
Cost			MediaWiki software is Free Software (as defined by it's license). Vendors charge for added value such as support and service. You pay per the seat for a Confluence license. There is a free option for open-source projects. There is a reduced price option for non-profit organizations. You also pay for add-ons that are included with MediaWiki (even simple ones like Title redirects!). You also pay for added value such as training. Some things are just not available at any price (e.g. customization).
Professional Support			MediaWiki has paid professional support provided by a long list of individual software developers as well as companies around the world Confluence has a variety of support options available through a single company (Atlassian in Australia) with full support starting at $35,000

Let's see who uses MediaWiki http://www.open-emr.org/wiki/index.php/How_to_Document_Your_Code_Properly

Gnu's Not Unix, because Unix is proprietary software while Gnu is software that respects your freedom.

General Public License = A sane copyright license

WikiMedia Foundation = the organization which runs various projects including Wikipedia.org