I think I managed to find what I was looking for.
After doing some serious research in here, on stackapps.com, I finally found what I was looking for, namely an easy way to get notified about new answers, posts and/or comments for the topics that I am interested in listed on all websites from StackExchange network.
The application is called StackTracker (a Cross-platform desktop notification app) and it has support for Linux, Windows and Mac OS X. It can be found and downloaded on this page, and it doesn't require user to login or enter a password or things like that. It works by simply entering the URLs of interest for the user, and it will just sit and wait in the system tray section to provide the user with desktop notifications for each new comment/answer to those topics entered before as URLs (web adresses from AskUbuntu, StackApps and I guess all the other websites listed on StackExchange network).