Nagios - Complete monitoring and alerting for servers, switches, applications, and services
Prometheus - An open-source systems monitoring and alerting toolkit.
Gitwin - Enable your Windows system as a powerful and secure Git repository. Supports ssh, http(s) transports. Gitweb with highlighter and gravatar support available.
Zabbix - Track, record, alert and visualize performance and availability of IT resources
NIXStats - SaaS monitoring tool for window/linux servers and websites. Think up-time robot but with more features.
Fluent Bit - Data collector and log forwarder.