Can Protractor be used to test any non AngularJS application?
Yes of course. The protractor is essentially a wrapper around the selenium webdriver for JavaScript (WebDriverJS) - so you get all the features of selenium - along with some additions and improvements that are definitely worth your time. Grunted - You get more from Protractor if you test an AngularJS app, but there is still a lot of good stuff for the rest of JavaScript apps.
I modified and posted a blog post to answer your question - see here:
http://testautomation.applitools.com/post/94994807787/is-protractor-easier-than-selenium-by-doron
Please note that this post does not provide a complete way. I'll go into more detail on how to overcome the bootstrap issue in future posts. A good place to start is here: http://ng-learn.org/2014/02/Protractor_Testing_With_Angular_And_Non_Angular_Sites/
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