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!

Community Questions for Confluence - Keep questions and answers in one place with an engaging, community-driven Q&A discussion forum, powered by Confluence

Zendesk - Zendesk is a beautiful, lightweight help-desk solution.

Question2Answer - A Q&A site helps an online community to share knowledge.

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

Stack Overflow for Teams - Everything you love about Stack Overflow in a private space.