Help, 2 urls for 1 site

[helfgott]

Hi people,

I've been developing an app in php.

I also have a website i,e:

mysite.com

I'd like to put that online app on the site so:

mysite.com/my_new_app

But i'd like to use a different URL instead mysite.com:

mysite.com/my_new_app = online_app.com

Is it against the rules of Adsense, Google, SEO? Is it a common practice or i have to get another server to host my app. (I don't want to use a sub-domain like mysite.online_app.com)

Thanks in advices.