Proper ways to contact US academics from outside academia? Forgive the question for being silly, but I do not live in the US and work in a different field.

I am developing an application I believe would be a wonderful (free) asset to the study and comprehension of a particular subject (history, which I suppose brings with it philosophy, sociology, and many others really) for students and docents alike.

I would thus like to gather the opinions of any number of actual professionals (maybe pique their interest and earn their cohoperation), who may be kind enough to waste a few minutes, on the concept, which is handily laid out in brief at the project's URL.

A quick look at a few universities' websites made it clear that is not the way, unless I wish to enroll.
I briefly considered contacting PhDs through LinkedIn, but it feels wrong.

So the question is:
what are the proper (sensible, respectful, appropriate, expected) ways and channels, if any, for a complete professional stranger, to contact a US Professor and hold some expectation that they may react after some fashion (or at least a suspect they may have actually received the message) ?


Why the US ?
Because it seems like a good starting point. There are so many people and learning institutions in the US. And American history is quite unique. And the geography is vast, it fits well with the concept. Plus, english.


The Answers all raise very helpful points, I wish I could pick at least 3. It being a question about new tech, students may be the ones to pursue. Thanks all.
I am developing an application I believe would be a wonderful (free)
  asset to the study and comprehension of a particular subject for
  students and docents alike.


Consider presenting it at an academic conference. In my field, there are usually industry booths at the conferences. But there is also often the opportunity to present innovative software with a poster, or sometimes even as a talk.

Don't expect any responses to unsolicited emails marketing your software. These will usually be regarded as spam.