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
LiveAgent - LiveAgent is a fully-featured web-based live chat and help desk software. It harnesses the power of a universal inbox, real-time live chat, built-in call center, and a robust customer service portal. Start your free 1 month trial today!
Confluence - Confluence is content collaboration software that changes how modern teams work
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.