A: How have you done this?
B: All alone.
Just about anything is possible in some context or other. As it stands, it doesn't strike me as very natural- what's your idea behind the question? I'd say 'All by myself' might work better, but it's still a strange question/answer pairing IMO.
Is it possible to say "all alone" if one is asked a question has he done it alone or was given a hand?
Have you done it all alone?
Yes, all alone. or simply
He has written all these procedures. All alone. (Nobody's helped him.)
I wonder is "all alone" in my language equal to "sasvim sam".(in Croato-Serbian)