Zabbix - Track, record, alert and visualize performance and availability of IT resources
Jenkins - Jenkins is an open-source continuous integration server with 300+ plugins to support all kinds of software development
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.
CircleCI - CircleCI gives web developers powerful Continuous Integration and Deployment with easy setup and maintenance.
Prometheus - An open-source systems monitoring and alerting toolkit.
Travis CI - Focus on writing code. Let Travis CI take care of running your tests and deploying your apps.