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
Zabbix - Track, record, alert and visualize performance and availability of IT resources
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.
Datadog - See metrics from all of your apps, tools & services in one place with Datadog's cloud monitoring as a service solution. Try it for free.
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.
Prometheus - An open-source systems monitoring and alerting toolkit.