Let me try to condense my experience with licensing from the distributor perspective into few points.


1. Choose a STANDARD license! Serious! NO exceptions.
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This is the list of options: http://www.opensource.org/licenses

These licenses are well understood. it is known how they can be combined, what is possible and what is not. Any custom license is potentially dangerous. Written by people who might not know what they are doing, might focus on a particular national jurisdiction, a particular use case, add unnecessary/uneffective usage restrictions, ... The outcome of this is avoidable hassle, complications with legal compliance, difficulty to create derived software, hindering legal distribution. What sounds like a fancy license in the US might be illegal in the EU.


2. Enforce free software culture OR encourage widespread use (unconditionally)
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The basic decision is: copyleft or not.

GPL-style licenses (copyleft) enforce "open-sourcing" of derived software. That has many benefits for humanity. Not naming them here ... (too many)

More permissive (non-copyleft) licenses (e.g. BSD-style) don't do that. The advantage is that it removes the need to come up with a more permissively licensed implementation that can go into proprietary products. It POTENTIALLY encourages collaboration instead of fragmentation. However, it needs more than a license to make that work.

If you want to have your code used as much as possible: Go permissive!
If you want to make sure your work only goes into something free and open (so you could benefit from it yourself): Go copyleft.


3. Trust the law
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Do not put stuff into a license that is not yours to enforce.

Adding "Not FDA certified: You must not use this in clinical practice" is not good/necessary/relevant.

Every person operating medical equipment for patient treatment knows that they need to restrict themselves to certified products. If they don't, they go to prision/pay lots of money/loose their insurance/job/ etc. Hence, they won't use non-FDA-certified products to start with. If they do nevertheless it is not your problem. Here is what the BSD license says about that:

... THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL ... BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES.

If you nevertheless put the above sentence in the licence, your software is no longer free software (even if the rest says GPL). Even if somebody would like to take it, and actually put it through a certification process they couldn't, because it says: "You must not use this in clinical practice" -- so why bother.

Always see (1)


4. A license is not the place for politics/moral
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Anything that restricts the freedom of use for ANY purpose turns software into a non-free product that makes it difficult to combine/derive/distribute. If you intend to develop free software, don't put:

"Must not use for nuclear bombs"
"Must not use for abortion"
"Must not use for animal research"

even

"Not for commerical use"
"Only for research"

will make it non-free! Instead of requiring "non-commercial" better go for GPL. "only for research" -> (3)

Always see (1)


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The Debian Free Software Guidelines (DFSG) represent a widely acknowledged, human readable, 10-point checklist to assess whether something is a "good" license (valid beyond the scope of Debian).

http://www.debian.org/social_contract#gu...