Unfurl a string

SOGL V0.12, 21 20 19 18 17 bytes

ø;[;ο⁴№č▓┼№TJι;jI

Try it Here! (→ added because this expects input on the stack)

Explanation:

ø;[;ο⁴№č▓┼№TJι;jI
ø;               push an empty string below the input           stack with the input GFE,HID,ABC
  [              while [ToS (the array) isn't empty] do       ["", [["G","F","E"],["H","I","D"],["A","B","C"]]]  
                                                                stack at the second time looping
   ;               duplicate 2nd from top                     [[[H,G], [I,F], [D,E]], "ABC"]
    ο              wrap it in an array                        [[[H,G], [I,F], [D,E]], ["ABC"]]
     ⁴             duplicate 2nd from top                     [[[H,G], [I,F], [D,E]], ["ABC"], [[H,G], [I,F], [D,E]]]
      №            reverse vertically                         [[[H,G], [I,F], [D,E]], ["ABC"], [[D,E], [I,F], [H,G]]]
       č▓          join the inner arrays (┼ fails otherwise)  [[[H,G], [I,F], [D,E]], ["ABC"], ["DE", "IF", "HG"]]
         ┼         add the 2 parts together                   [[[H,G], [I,F], [D,E]], ["ABCDE", "   IF", "   HG"]]
          №        reverse vertically again                   [[[H,G], [I,F], [D,E]], ["   HG", "   IF", "ABCDE"]]
           T       print that without popping                 [[[H,G], [I,F], [D,E]], ["   HG", "   IF", "ABCDE"]]
            J      take the last line off                     [[[H,G], [I,F], [D,E]], ["   HG", "   IF"], "ABCDE"]
             ι     remove the rest of the array               [[[H,G], [I,F], [D,E]], "ABCDE"]
              ;j   remove the last line of the original array ["ABCDE", [[H,G], [I,F]]]
                I  rotate it clockwise                        ["ABCDE", [[I,H], [F,G]]]

Python 2, 209 207 205 203 202 201 200 196 bytes

-4 bytes thanks to @Quelklef!

s=input();l=len;k=''.join;exec"print s;s=[x for x in[' '*l(s[0])+k(x[:-1]for x in s[-2::-1])[t::l(s[0])-1]for t in range(l(s[0]))][:-1]+[s[-1]+k(x[-1]for x in s)[-2::-1]]if x.strip()];"*(2*l(s)-1)

Try it online!

Python 2, 219 217 215 213 212 211 207 bytes

s=input();l=len;k=''.join;exec"print'\\n'.join(s);s=[x for x in[' '*l(s[0])+k(x[:-1]for x in s[-2::-1])[t::l(s[0])-1]for t in range(l(s[0]))][:-1]+[s[-1]+k(x[-1]for x in s)[-2::-1]]if x.strip()];"*(2*l(s)-1)

Try it online!

The first one outputs as a list of Strings, the second one outputs as ASCII-art.

Charcoal, 42 35 bytes

ＡＥθＳθＷ⊟θ«⪫θ¶ＡＥι⮌⪫Ｅθ§μλωθ⊞υι↙←⮌⪫υωＤ⎚

Try it online! Link is to verbose version of code. Edit: Saved 7 bytes mostly by switching from character arrays to strings. Explanation:

ＡＥθＳθ

Read the input square as an array of strings into the variable q.

Ｗ⊟θ«

While the last string in the array is not empty, remove it.

⪫θ¶

Print the rest of the array.

ＡＥι⮌⪫Ｅθ§μλωθ

Rotate the rest of the array by looping through each character of the last string and joining the lth character of every remaining string in the reversed array.

⊞υι↙←⮌⪫υω

Append the previously removed last string to u, which holds the unfurled value, and print it.

Ｄ⎚

Output the result and then clear the canvas ready for the next iteration.

Note that this version outputs the final unfurl on a separate line, if this is undesirable then for 38 bytes:

ＡＥθＳθＷ⊟θ«⊞υι←Ｅ⁺⟦⪫υω⟧⮌θ⮌κＡＥι⮌⪫Ｅθ§μλωθＤ⎚

Try it online! Link is to verbose version of code. Explanation: ←Ｅ⁺⟦⪫υω⟧⮌θ⮌κ reverses the current array, prepends the unfurled line, then reverses the characters in each line, then prints everything upside-down, thus producing the desired result.