My List: Oxidized as a replacement for RANCID Telegraf + InfluxDB = Tons of Grafana Dashboards (Open Source Slack Alternative) Ansible or Python Knowledge with Paramiko or netmiko for network automation.
BGP: FRRouting - Mimics Cisco CLI BIRD - Programming style config format. Exabgp - Mostly used for API driven applications, monitoring with heartbeat scripts. (many others) DDoS detection and/or filtering: Fastnetmon - Supports many methods for packet processing. Ddosdetector (IPv4 Only) - Uses netmap for packet processing. Top Talkers + Other Creativeness (like fib compressing, or route optimization): pmacct - sflow/netflow combined with BGP, and a database backend Servers: Sensu or LibreNMS for Nagios type monitoring. Diagnostics: MTR - ...and knowing how to interpret it's output. -Ryan