Similar License Like 'Creative Commons BY-NC-SA', But For Software ...

I'm not aware that github imposes any requirements on how your code is licensed, beyond stating that "you agree to allow others to view and fork your repositories" (https://help.github.com/articles/github-terms-of-service).

So, you can almost use any licensing conditions you want. If you drop a file named "LICENSE.txt" in your repository, most people will get the message. If people ignore the message, either ignore them, or consult your lawyer and be prepared to pay him/her.

If you stray away from the "standard" licenses, however, your code will be less useful to others.

The classical "BY-SA" license for software would be the GPL. It is not a BY-NC-SA license, but among popular free software licenses it is probably one of the most "restrictive".

When you put your software under a free/open-source license, you are not giving up any rights. You (irrevocably, in most cases) grant some rights to others. This is an important distinction, because you always keep the right to use your own software commercially.

If you want to sell your software as proprietary software later, you can simply license it under a different (proprietary license) in addition to the free software license you've decided on. You can't "recall" published free versions, but you don't need to make any of your future improvements available as free software.

There are several different ways in which other people might make money off your software:

• They might develop a new and improved version of your software and sell it as proprietary software (you don't get to see or use their improvements without paying!). The GPL prohibits this (if you wanted to allow that, you'd use a "non-copyleft" license, like the BSD or X11 licenses)

• They might sell your software, unchanged, bundle it with books or otherwise redistribute it for money. The GPL allows this, but this is a good thing in many ways, as you might get a free-of-charge distribution network. There's not a lot of money in this anymore nowadays, as people will just download the software (for free) instead. There may be some obscure free software licenses that prohibit that.

• Someone might offer to improve the software, but demand money for his work. This is OK, as the results of the paid-for work will afterwards be available to everyone free of charge. I don't see how a license agreement can possibly prevent this.

• Someone might offer support contracts for your software. Again, I don't see how you could (or why you would) prohibit this. If you allow me to use your software, I can pay someone else to help me use it.

• When you decide to sell a new-and-improved proprietary version of your software, someone might improve the free version of the software and compete against you, undercutting your price. They don't really make money from it, but you might not like it. Free/Open Source licenses are non-revocable (by definition, I think), so you can't do much about it (revocable freedoms are no freedoms at all).

• Someone might use your software, and might make money doing it. Prohibiting this contradicts both the Open Source Definition (http://opensource.org/osd.html/ Point 6) and the Free Software Definition (http://www.gnu.org/philosophy/free-sw.html "Freedom 0"). A free software program does not have small print attached that tells you how you may and may not use it.

Summary: Consider the GPL. It is the strongest popular license on the ShareAlike front. If you want to be more restrictive, your code won't really be that free anymore, and people won't be able to combine your code with other (e.g. GPL-licensed) code.