App for analyzing installers

Is there an app which shows contents of a .pkg file and shows which files an installer copies to my mac, what scripts it runs and so on?

Yes, there's a shareware app called Pacifist ($20). I've used it for years, and it works wonderfully well (even on old Macs).

Alternatively, you can download a free QuickLook extension for blazing fast previews of packages. It's called SuspiciousPackage.

You can extract package files and sort through their contents without actually installing them. To do this, you can often just right-click on a .pkg file and select “Show Package Contents” – but that isn’t always displayed.

If that option is unavailable, you can extract .pkg files using a command line tool called pkgutil that is bundled with OS X. Launch Terminal.app and enter the following:

pkgutil --expand /path/to/package.pkg /output/destination/

Hint: you can drag & drop items into the Terminal to print their full path, making this tip easier by typing: pkgutil –expand [drop file here] /destination/path/.

After that, you can go to the output path in the Finder and check out the extracted files.

Source