Licenses, licenses, licenses ...

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Are you writing software that that you plan to distribute? If so, you need to take a look at the licensing options that are available to you. [X-Archetypes]

Yes, it's true, folks - the GPL isn't the only open source license around.  A quick guide to it and some of the other popular choices:

GPL: Code licensed under the GPL may only be mixed with other code under the GPL.  That means if you want to reuse code from a GPL-licensed app and release a binary, you need to release the resulting source code under the GPL.

You can charge money for GPL-licensed software, but recipients always have the right to copy and distribute the source and binaries.

Choose the GPL for your app if you want to ensure, at all costs, that the source for all derivative works will remain open.  If you don't want companies to be able to make enhanced (closed source) versions of your software, use the GPL.

Linux is released under the GPL.

BSD / MIT / X11: These licenses, collectively referred to as 'the BSD-style licenses' impose fewer restrictions on what you can do with the code.  Basically you can do what you like with it as long as:

1. You properly credit the author (you don't claim you wrote it yourself)
2. You don't sue the author if something goes wrong
3. (With the BSD license) you don't use the name of the software or author in your advertising.

Choose one of these licenses if you're not concerned about people including your code in commercial software and not releasing the source.  Sometimes you want to encourage commercial exploitation of your code -- that's the time to use a BSD-style license.

PyCS is released under the MIT license.  FreeBSD is released under the BSD license.  Mono's class library was released under "an X11-style license" and now seems to be available under the MIT license.

Artistic License: This is similar to the BSD-style licenses, except that it makes a bigger deal of the name of the software.

You can copy 'Artistically Licensed' code and include it in your software as long as you don't use the original name.  You are only allowed to use the name of the software if you distribute the 'standard version', i.e. the official one, released by the author.

Choose this license if you are concerned about other people passing off their software as yours, but not worried about enforcing the 'openness' of derivative works.

Perl is released under the Artistic License.  If you modify Perl, you have to call it something else, e.g. 'Not Perl'.

Disclaimer: This isn't legal advice, just my own take on what the licenses mean.  For the whole truth, read the licenses yourself.

Related information

BSD vs. GPL: A Framework for the Social Analysis (Dr. Nikolai Bezroukov) talks about the social issues surrounding the choice of a free software/open source license.

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