HelpScout - Help Scout is a simple, straightforward way to provide excellent support

Stonly Knowledge Base - Interactive knowledge bases and help-centers

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

Free Knowledge Base by Dashly - Optimize your customer support with Knowledge Base by Dashly

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

Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.