I previously kept Grab.app on Mojave 10.14 by simply copying it over from High Sierra 10.13. I prefer the simplicity of Grab over the new Screenshot.app, and I hate that Screenshot adds a drop shadow.
Alas… Grab from High Sierra 10.13 is dead on Catalina 10.15, as Apple did not maintain backward compatibility in AppKit. RIP.
For screen shots “my way”, see my Touch Bar Quick Action (Automator script), which uses the screencapture command line - without shadow, without the loud “snapshot” sound effect. You can even use Automator to create your own .app that leverages the command line!
Updated 19 Mar 2020: A quick tip with Screenshot.app: I hate that it captures window shadows. To turn it off, open Terminal and issue this command:
defaults write com.apple.screencapture disable-shadow -bool true
Undoing it is simply replacing true with false.