I’m not really seeing much in the way of cybersecurity tools in this thread. These are all FOSS and usable without extra cost (although some have paid upgrades)

• Zed Attack Proxy is something I use pretty regularly.
• Snort is a great IPS.
• Metasploit works great with some extra tooling.
• ClamAV is the Linux standard.
• Fail2ban is great for hardening.
• Crowdsec has replaced Fail2ban for a lot of folks.