MediaWiki - MediaWiki is a free software wiki package written in PHP, originally for use on Wikipedia.
Freshdesk - Freshdesk is a cloud-based customer support software that lets you support customers through traditional channels like phone and email, social channels like Facebook and Twitter, and your own branded community
TiddlyWiki - a non-linear personal web notebook
Zoho Desk - Industry's first context-aware Helpdesk Software
Confluence - Confluence is content collaboration software that changes how modern teams work
Salesforce Service Cloud - Service Cloud integrates customer service with social networks and provides a self-service customer portal and knowledge base system.