Malwarebytes
Recommended for EVERY Mac user. This app is so easy to use and it runs automatically. Malwarebytes protects your Mac from malware, adware, ransomware, fake website, and more. The best part about this app is that unlike antivirus software it will not use up all of your system resources!
Clean My Mac X
If you need to clean up your Mac, I'd recommend watching my class (link below) which will help you with the initial process, but Clean My Mac X does a good job of finding the many smaller flies that can take up space. The new version also includes Malware protection.
Photolemur 3
If you enjoy photography, but DON'T enjoy spending a ton of time retouching your photos, Photolemur 2 is for you. It's a one-click solution to make your photos look their best.
Last Pass
Passwords suck. Last Pass makes it suck less. Works with every operating system out there, installs into your web browser, and let's you share passwords with loved ones (making it a wonderful solution as a type of "digital will")
Microsoft OneNote
Microsoft OneNote is a great tool for business professionals and students. It's a competitor to Evernote, but in resent years, I've favored OneNote over Evernote. It's also Free!
Magic Window 4K
I just love this app especially on any Mac with a 4k or 5k display. It transforms your boring desktop background into beautiful time-lapse photography from all over the world.
VLC
This is a great free media player to keep on your Mac. Anytime you run into obscure video formats, this tends to play everything.