Is it possible to run .pkg files in Ubuntu or Fedora. If so, how do I start with it?
What's .pkg file? It's a file format used in Mac systems(Apple Inc.)
Is there any alternatives which can run .pkg files in Linux distros? ( specifically Ubuntu or Fedora, I'm using latest version in both distros).
Answer
You can unpack the Xar format using the xar archiver; perhaps the ark archive front-end can also handle the Xar format, as it links against libarchive12, which provides read-only support for the Xar format.
OS X uses the Mach-O executable format, while Linux uses ELF. (Okay, Linux can also read some archaic a.out formatted files too, but this format is effectively dead on modern Linux systems.) There is an experimental Mach-O loader for Linux, but it sure sounds like a toy at this point. (You'd also need the libraries that applications use in order to actually run programs -- that'd be another complication.)
So: Yes, you can unpack them. No, you cannot simply run OS X applications on Linux.