Is the "$?" (dollar-question mark) variable available only in the Bash shell?

The $? exit-code is common to any shell that follows POSIX, and is described in 2.5.2 Special Parameters:

?
Expands to the decimal exit status of the most recent pipeline (see Pipelines).

As Thomas Dickey said, any POSIX shell (ie. pretty much all of them) will have $?.

This question interested me quite a bit, so I tested it on any shell I could get my hands on:

• mksh
• zsh
• /bin/sh on my Samsung Galaxy S5
• /bin/sh on my router
• tcsh
• ksh
• dash
• /bin/sh on my virtual UNIX System V from 1989 or so
• cmd.exe and powershell.exe on my Windows 10 computer

and $? worked in all of these but fish and cmd.exe.

Found two interesting things:

1. $? works in Windows PowerShell!

Well, to a point. Instead of returning 0 or a higher number, it's just True and False.

PS C:\WINDOWS\system32> echo $?
True
PS C:\WINDOWS\system32> gfdhgfhfdgfdg
gfdhgfhfdgfdg : The term 'gfdhgfhfdgfdg' is not recognized as the name of a cmdlet, ...(big long error output).....
PS C:\WINDOWS\system32> echo $?
False

2. $? doesn't work in the shell fish.

However, when you type $? in fish, you get this message:

~$ echo $?
$? is not the exit status. In fish, please use $status.
fish: echo $?

I haven't used it much but I'm not surprised, fish seems to have its own interesting shell language, completely different from bash or whatever.