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Choosing a License

Do not write a new license if it is possible to use one of the ones listed here. The propagation of many different and incompatible licenses works to the detriment of Open Source software because fragments of one program cannot be used in another program with an incompatible license.

Steer clear of the Artistic License unless you are willing to study it carefully and edit out its loopholes. Then, make a few decisions:

Do you want people to be able to take modifications private or not? If you want to get the source code for modifications back from the people who make them, apply a license that mandates this. The GPL and LGPL would be good choices. If you don't mind people taking modifications private, use the X or Apache license.
Do you want to allow someone to merge your program with their own proprietary software? If so, use the LGPL, which explicitly allows this without allowing people to make modifications to your own code private, or use the X or Apache licenses, which do allow modifications to be kept private.
Do you want some people to be able to buy commercial-licensed versions of your program that are not Open Source? If so, dual-license your software. I recommend the GPL as the Open Source license; you can find a commercial license appropriate for you to use in books like Copyright Your Software from Nolo Press.
Do you want everyone who uses your program to pay for the privilege? If so, perhaps Open Source isn't for you. If you're satisfied with having only some people pay you, you can work that and keep your program Open Source. Most of the Open Source authors consider their programs to be contributions to the public good, and don't care if they are paid at all.
Table 12.1 gives a comparison of licensing practices:

Table 12.1: Comparison of licensing practices.
License Can be mixed Modifications can be Can be Contains special privilege
  with non-free taken private and not re-licensed for the original copyright holder
  software returned to you by anyone over your modifications
LGPL X      
BSD X X    
MPL X X    
Public Domain X X X  

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Last updated: 1999-08-06