CC BY-NC-ND 3.0
http://creativecommons.org/licenses/by-nc-nd/3.0/
The creative commons licenses were not intended for open source software in particular, but can be applicable to software still - and for such purposes. In essence your freeware program would be a work of art that you want to be shared freely. And the -noncommercial tag as well as the -noderivatives rule would match your intent.
Attribution-NonCommercial-NoDerivatives
This license is the most restrictive of our six main licenses, only allowing others to download your works and share them with others as long as they credit you, but they can’t change them in any way or use them commercially.
Short answer: absolutely not.
Everything a person writes, whether it is software or text, is automatically under copyright. The default state of any text is that it is completely owned by the author and no one has rights to do anything with it without express permission of the author. A few decades ago, an author used to have to assert copyright in order to retain it, but this is no longer the case.
You can even see on sites like this legal text down there that states that I agree that this post I am typing is available under a certain license. If that wasn't there, I'd retain all rights under the law.
Thus, if you cannot find any license information, then you cannot copy or modify it for any reason other than personal use.
Making something "open source" is a deliberate act and for you to treat it as such, you have to have found a license that tells you explicitly what your rights to the software are. This is even true of "public domain" software. That is, something is only "public domain" if it has either expired copyright (which mostly means it was written decades ago) or if the author has explicitly placed it in the public domain in writing.
In the case you describe, your only recourse is to contact the author and request that he allow you to do what you ask. To do otherwise is flatly illegal and in theory could lead to damages. (In practice, of course, you'd have to get caught.)
Edit: IANAL. Talk to one if you intend to do this.
Best Answer
NO.
YES.
In all 166 nations that are signatories to the Berne Convention, copyright is granted to an author when the work is created. The author holds a monopoly on all copyright rights (creating modifications, creating and distributing copies, etc.). You -- as someone who is not the author -- have been granted none of those rights.
A license is a mechanism by which the rights-holder (here, the author) grants some set of rights to a recipient (here, you). You say that the author has not offered any license, which means by default that the author has reserved all of his rights. The fact that the author has made his code publicly viewable does not mean that you have been granted any rights beyond the right to view the code. The right to make derivative works and the right to redistribute the code are not rights that you currently have.
Since you mention that code is on Github, it's worth mentioning that the Github TOS have this to say about material hosted on their site:
Hosting on Github means that the author grants others the right to "view" and to "fork" the repository. Here, "fork" probably just means "use Github's fork feature", which creates a repository clone, hosted on Github. I admit the Github's use of the term "fork" here is ambiguous, but if my reading is correct, then in no way does this appear to grant you any right to:
The bottom line is: you don't have the right to distribute this code. It's possible that the author wants people to use his code freely, but neglected to include a license. Tell the author that the lack of a license has blocked your use of the code, and encourage the author to add a some mainstream OSI- or FSF-approved license to the repository.