Polycops and Robbers (Cops' Thread) This is the cops' thread, the robbers' thread is here
A polyglot is a program, that without modification, can run in multiple languages.

Allowed languages
Any language that was made before the challenge and isn't made for the purpose of the challenge, it is allowed, though discouraged, to use languages that are easy to recognize

Cops' Challenge
To write a non-empty program that does one of the following tasks:

Adds two numbers from STDIN
Prints &quot;Hello, World!&quot;
Prints the first 20 terms of the Fibonacci sequence

Then, list the languages it works in (it must do the same thing in all languages). When you first post your answer, it is vulnerable, and robbers will try to find more languages it works in other than the ones you specified. If any robber finds a language, they comment on your question saying they cracked it. You should then edit your question saying it got cracked and list the languages you were missing.

If a week passes by and nobody cracked your submission, you can mark it as safe, no robbers can crack it.

Winning
Most upvoted safe answer is the winner.

Extra rules
Cops must know there is a language that the program runs in other than the ones they wrote, so that there's a guarantee that all answers are possible to crack.
And as always, standard loopholes apply.
Wow, cracked by Jo King while I'm still typing the explanations lol

'&lt;?php '//'; #@ SPELL,WITH,ME, ,H,E,L,L,O, ,W,O,R,L,D,&quot;'Hello, World!'&quot;
$a = &quot;'Hello, World!'&quot;;
if ([])
 console.log($a);
else {
 for ($i = 1; $i &lt; strlen($a) - 1; $i++)
  echo($a[$i]);
}
// ?&gt;'

Prints 'Hello, World!' (with single quotes) in both JavaScript and PHP. This should be an easy one to solve.
How this works
'&lt;?php '//'; #@ SPELL,WITH,ME, ,H,E,L,L,O, ,W,O,R,L,D,&quot;'Hello, World!'&quot;
JS treats this line as a string '&lt;?php ' followed by a // comment, and PHP prints ' (outside the tag, so literally), then starts the script with open tag, and a string '//', then a # comment.
$a = &quot;'Hello, World!'&quot;;
Both JS and PHP defines the variable a to be the string &quot;'Hello, World!'&quot;.
if ([])
 console.log($a);

In JS, since [] is consider truly, console.log($a) is executed and this prints out the string `&quot;'Hello, World!'&quot;.
else {
 for ($i = 1; $i &lt; strlen($a) - 1; $i++)
  echo($a[$i]);
}

In PHP, since [] is consider falsy, the for loop is executed and this prints out the characters Hello, World! (notice the absence of quotes) subsequently.
// ?&gt;'
In JS this is a comment, but in PHP the close tag ends the script and the ' after the tag is printed out literally.

Yes, the remaining language is Befunge-93.
'&lt;?php '//'; #@ SPELL,WITH,ME, ,H,E,L,L,O, ,W,O,R,L,D,&quot;'Hello, World!'&quot;
&lt; redirects the IP to the end of the line, then &quot;'Hello, World!'&quot; is pushed in reversed order. After that the 15 ,s are used to output the characters (in normal order because of the double reversal). Finally @ terminates the program.