I still use DOS. Or at least I use "Command Prompt" on my Windows computers. 'dir' and 'cd' are the main ones I use from the command shell. And I use the command prompt all the time on my linux computers.
Gatac's list is good, but there's a great DOS command he didn't list: 'rem.' It's 'echo' without the output! Let's look at a typical novice's session with the mighty rem:
c:\> rem
c:\> rem help
c:\> rem quit
c:\> rem exit
c:\> rem bye
c:\> rem hello?
c:\> rem eat flaming death
c:\> rem ^C
c:\> rem ^C
c:\> rem ^D
c:\> rem
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Note the consistent command flags and error reportage. Rem is
generous enough to flag errors, yet prudent enough not to overwhelm
the novice with verbosity.
(Okay, I started borrowing from
The Ed man joke page at the end there.)