Could someone tell me about the application of invitation letter for tourist visa for my friend (who is not in EU zone). Is there online form available which I can download, and fill it with required documents. I tried to find such forum in migration website but unable to find any.
There isn't any particular form for that. You basically have to write it yourself and explain how his/her travel costs will be covered, why they're coming, where they're going to live and that you assume responsibility in the event they do not leave the country when their visa ends (sometimes they may call you to hear that).