The .dmg format has been used for years and is almost as old as OS X itself. They're also used by pretty much any major third party developer for OS X that you can think of, either to deliver their software products or updates. You can easily buy any number of shareware or freeware apps for both Windows and OS X to create/open/extract/manipulate them.

What I do know, from commentaries voiced by shareware developers on forums, is that the major problem with .dmgs (as well as earlier virtual disk image formats commonly used by Apple like .img) is that many end users wound by being confused by the idea of virtual disk images. All too often people would just run the application from the .dmg without copying it to their hard drive, then would be perplexed when, after a reboot, the app would be gone (since the system would have unmounted the virtual disk). Either that or they couldn't understand why they couldn't delete a .dmg that was in use by the system. I've encountered this myself with Mac users for whom I've consulted. .pkg files on the other hand, are pretty straight forward. You double-click them, and that's it.

My best guess (and as with anyone else's reasoning, it's just a guess, barring official word from a Blue), is that they moved to .pkgs because, frankly, of silly PEBKAC problems with end-users who couldn't figure out how to properly install games to their hard disk. I can also guess that .pkgs might also make installation easier for games -- especially indie games -- that make use of dependencies like Mono, OpenAL, or SDL. Oh yes, you can. My weapon of choice is Pacifist, a shareware app ($20) that allows you to look into .pkg files and manually extract anything you want out of them. I actually haven't used it for a while, but IIRC it's mainly nagware; the core functionality is something you can freely utilize without paying.

Huh. I've never encountered that problem and it's also the first time I've heard of such, but I'm wondering whether it is at all related to some kind of security/admin settings. ... Could it be possible that a third-party program running in the background may be interfering somehow?

I tried that installer, ftl__advanced_edition_enUS_1_6_7_18662.pkg, and it installed fine. It asked for the disk/volume (picked the 2nd one in my case) and later asked for the folder (picked a non-standard folder on the 2nd disk). After the installer was finished FTL is sitting in said folder.

Does anyone know in which temporary directory the app is unpacked before it is moved to the destination directory?

The pkg installer extracts the files in:

/private/tmp/PKInstallSandbox.xxxxxx/Scripts/com.gog.pkg-installer.xxxxxx/payload
(xxxxxx = random Hex values)

At the moment during the installation in which the window for location selection pops up, this temporary folder contains the complete data of the app ("Contents/...", 10 GB in my Test, tides_of_numenera). After I select the location this temporary folder disappears - but I don't find the app in the selected destination directory...

In the scripts of the installer you can find:

gog_bundle_name="Torment Tides of Numenera.app"
gog_bundle_location="/Applications/"
gog_full_path="${gog_bundle_location}${gog_bundle_name}"
mv payload/* "${gog_full_path}"

It seems this payload folder is simply moved to the destination location with the name of the app - but not in my case :-(
If I move the folder by hand, then it works and I can play the game...
Why this "mv" operation fails?

When all files are extracted (ie. before you select the destination folder), open the terminal to the folder the script is in, and run the script (by typing "./<scriptfilename>"). Does it produce any output in the terminal? Are the files moved to where they should be?

Did you find this other thread?
PKG installation issues on Mac OS X

It says something about a separate dialog for choosing the folder, after choosing the disk. At first someone said the dialog appeared near the beginning of the installation, and then several months later (3rd post) someone else said the folder dialog appeared near the end of installation.

I found a workaround for this mysterious bug: Ignore the destination selection pop-up. After some minutes the installer reports a succsessful installation (pop-up window remains open). It seems there is a timeout - and if no location is selected, the installer chooses the /Applications path and finish the installation by itself. And then I can found the app inside the /Applications folder. But if I select the /Applications folder manually, then the app disappears when copying...

Hi people :)
I bet all Mac users have had the same problem by now. Just in case anyone coming here has not yet found an answer, this is the workaround I got from a fellow GOGian (who in turn got it from a Blue):

.PKG does not install game eventhough it says it installed successfully.

In case you don't want to follow another link, here's the workaround described in that thread:

WORKAROUND SOLUTION
So, if anyone has trouble with the installer NOT installing the game eventhough it says it did, this is what you should do to unpack the .pkg file and run the game yourselves:

1. Open Terminal and write:

xar -xf <package_path>
cd package.pkg
tar -xvf Scripts

The <package_path> is the location in your computer where you currently have the .pkg file of the game that is misbehaving.

2. Press Enter and let Terminal do its thing ( it could take a while to even start doing anything, so be patient ).
3. Look for a newly creted .pkg file inside your User accounts. It will be called package.pkg
4. Right-click the package.pkg file and select Show Package Contents.
5. Search around for a folder named payload.
6. Copy or move that folder to any location you like in your computer ( Applications or elsewhere ).
7. Rename the folder to whatever you like with the extension .app ( E.G. Shogun.app ).
8. That's the game, so double-click that file to start.

I hope this helps.
:)

Thanks. This works for me with a clean-installed macOS Mojave when I was adding back 2 of my my GOG-bought games - Fez and Hyper Light Drifter. I didn't have this problem previously with High Sierra.

I think we should report this Mac OS installer bug to the support. The guys from gog don't read this forum.

The problem still exists

Excellent!! I had been looking for a method to avoid running the installer at all and this worked perfect. Thanks to the original poster of the solution and to you for re-posting!