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

UseResponse - Open-source, self-hosted customer feedback software, live chat and helpdesk system that you can install on your server. Organize documentation using knowledge base and get feedback from social networks with centralized system

Flarum - Flarum is the next-generation forum software that makes online discussion fun. It's simple, fast, and free.

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

UserVoice - UserVoice integrates easy-to-use feedback, helpdesk, and knowledge base management tools in one platform that empowers users to speak and companies to understand.

Discourse - Discourse is an open source discussion platform built for the next decade of the Internet.