RDM - This fantastic tool allows me to set my 4K Dell displays to be in Retina mode even though macOS won't natively do it. I also use it to change my resolution for streaming.
Reminders - The recent massive update to Reminders for iOS 13 & macOS Catalina has made it a heck of a contender with other todo apps.
Safari - Testing of websites but also to take beautiful screenshots of them with the browser wrapping it.
Slack - Majority of my community communication comes from Slack teams.
Stay - Use in conjunction with Mosaic to keep my windows tiled how I want them depending on what configuration I have set for the displays connected.
Synergy - I have my mid 2015 MacBook Pro clamshelled and tucked away with two displays hooked up as my main workhorse, and my 2017 MacBook Pro is propped up next to my displays and I use Synergy to share a keyboard & mouse between them.
TablePlus - To handle all my administrational needs for databases such as MySQL, PostgreSQL and Redis.