Prometheus - An open-source systems monitoring and alerting toolkit.
productboard - Beautiful and powerful product management.
Nagios - Complete monitoring and alerting for servers, switches, applications, and services
FastNetMon - FastNetMon is a very fast DDoS analyzer with sflow/netflow/mirror support.
StatsD - Simple daemon for easy stats aggregation.
ProdPad - ProdPad helps your team gather ideas, surface the best ones and turn them into product specs, and then put it all on a product roadmap.