Survicate - Collect feedback on your website and find out more about your visitors.
Kayako - Help Desk Software and Customer Service Software by Kayako. Improve customer satisfaction, increase sales.
Helprace - Helprace is a customer service software suite linking a ticket system with help desk software, giving customer support agents a complete helpdesk solution.
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.
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
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