Protect My Privacy (PMP) for Android

Protect my Privacy for Android allows you to deny or fake access to data on a per-app basis on your Android phone.  It is developed by Carnegie Mellon University.
http://www.android.protectmyprivacy.org/

DKIM validation tool and DKIM/Exchange Setup

Send an email from your DKIM-configured server to an address at https://dkimvalidator.com, and the site will give you a breakdown of what is or isn't working with your DKIM signing.

If you use Exchange, the open source DKIM signer for Exchange is a godsend.

DNS Utilities

IntoDNS runs an analysis on multiple aspects of your DNS, and tells you what isn't working.
https://intodns.com

MXToolbox will help you get your email records (SPF, DMARC and DKIM) straightened out, and offers a free weekly summary of your mail DNS health.
https://mxtoolbox.com

Google Postmaster tools can help you troubleshoot issues with sending mail to Google.
https://www.gmail.com/postmaster/

DNS

PowerDNS can store all DNS data in a MySQL or PostGreSQL backend, making synchronization between name servers happen via MySQL replication.  The add-on PowerDNS-Admin Web GUI makes for easier administration.  It isn't plug and play, but it is an alternative to BIND.
https://www.powerdns.com/

Technitium is another open-source project.  This one runs natively on Windows too.

VinylDNS, also on Github, provides a portal and API for DNS management.

Teleport, a replacement for OpenSSH

Teleport offers some interesting security features and aims to deliver a more unified view of the varioius systems (local, AWS, somewhere else) you have to manage.  Oh, and kubernetes something something too.

https://gravitational.com/blog/introducing-teleport-4-point-3-modern-replacement-for-openssh/

Ventoy is the tool you want for making bootable USB drives

Hey this is better than YUMI, which I mentioned a few posts ago. 

Install the tiny Ventoy on a USB drive.  Then to add different ISO images for installation, simply copy the ISO to the drive.  Nothing to install, just copy it.  When booted, Ventoy presentsa list of the ISO files on the drive boot from, and away you go.  Great way to have multiple OSes and versions on one drive.

https://www.ventoy.net

QB64 (Quick Basic 64)

Write programs in basic that get compiled to run in native binaries on Windows, Linux and OSX!
https://www.qb64.org