MediaWiki
Used by 4 peoplemediawiki.org ↗

“I help build, design, and maintain the MediaWiki software, currently focusing on web performance.”
Timo Tijhof Interview, Principal Engineer (Wikimedia Foundation) · via Uses This 
“As part of my work at Red Hat and as part of my participation in theFedora community, I work with several MediaWiki installations.”
Máirín Duffy Interview, UI designer, usability tester (Red Hat, Fedora) · via Uses This