GreyNoise IP Checker

GreyNoise has a web site that checks the external IP address in question to determine if malware was been detected in the past.

https://check.labs.greynoise.io/

https://www.bleepingcomputer.com/news/security/greynoise-launches-free-scanner-to-check-if-youre-part-of-a-botnet/

Technitium DNS Server

Technitium DNS Server is available for multiple platforms and offers a web-based dashboard.

https://technitium.com/dns/

https://www.howtogeek.com/block-ad-traffic-and-speed-up-your-browsing-with-these-3-free-open-source-dns-tools/

Mailspring

Mailspring is an email client that offers a basic edition for free.

https://www.getmailspring.com/

https://www.howtogeek.com/i-replaced-outlook-with-this-open-source-email-client-and-it-is-not-thunderbird/

RaspAP

RaspAP is a Linux distro that is designed to make a Raspberry Pi as a router.

https://raspap.com/

KSnip

KSnip is a cross-platform screen capture utility.

https://github.com/ksnip/ksnip

https://www.howtogeek.com/3-tiny-open-source-apps-that-pack-a-ridiculous-amount-of-power/

Cayosoft Guardian Protector

Guardian Protector is a free agent-less monitoring solution that delivers insight across Active Directory, Microsoft Entra ID, and Microsoft 365 services.

https://petri.com/cayosoft-guardian-protector/

https://www.reddit.com/r/CayosoftGuardian/wiki/howto/