Know your short cuts
DownloadCheatSheet 1.2.7 (It's free)
Requires macOS 10.9 or later
Just hold the ⌘-Key a bit longer to get a list of all active short cuts of the current application. It's as simple as that.
Create invoices and estimates on your Mac.
Time tracker for Mac OS.
Usage is another great application. And it's free as well.
Check out "Usage"