For example, mdfind lets you use Spotlight search on the command line. diskutil powers "Disk Utility.app". pkgutil lets you install .pkg files and also get information about programs installed that way. screencapture lets you take screenshots from the command line (you can specify which windows, etc.)
Anyhow, there's a bunch.
There are also random useful executables not in $PATH. This program powers your WiFi menu:
Nitpick: In general, the graphical tools don’t literally invoke the command-line tools. Rather, both the graphical tool and the command-line tool use the same C or Objective-C API (usually private and undocumented) provided by some system framework. But the command-line tools do tend to be more direct reflections of the underlying API, and more flexible.
If you like those, see also, off the top of my head and in no particular order: system_profiler, ioreg[1], networksetup, afconvert, sips, osascript, lsregister[2], apfs.util[3], and, from Xcode, GetFileInfo and SetFile.
All have man pages except lsregister; lsregister with no arguments shows help (for context, lsregister is useful when file icons / associations get messed up).
[1] A GUI version is also available as IORegistryExplorer.app in the Xcode "Additional Tools" packages available from
Pro-tip (at least for me): control (^) doesn't change this, so you can just hold all the modifier keys rather than trying to remember which 3 let you paste as plain text.