How to Invoke a External URL directly from Action or Report?

What do you mean with "invoke". There is a plugin that allows you to do HTTP requests. This is quite handy for integrating other systems that are not accessible by SQL or Webservice.

For Example i want to open www.appian.com in a New Tab from an Action or Report.

The SAIL linkField should help you. When used with the saveLink function you should be able to open most URLs.

forum.appian.com/.../SAIL_Components.html

It is available on 7.6 too.

Thanks stefanh, Can't i open link from Action or Report ?

I am not sure what you want to achieve. When you say "action" do you mean a related action for a record. Opening a link directly is not possible but you could put that link on the record dashboard itself or create a process that only shows this link in the start from and use that as related action.

From Action tab you can only provide link to start the process. For details refer the link, forum.appian.com/.../Adding_Tempo_Actions_to_an_Application.html.
In your process you can have a form, where you can place the safelink for external url.