Github has just released a great overview of all of the major licensing models in order to help you make a more informed choice:
I'm not an attorney. You should talk to one.
With that out of the way - there are too many free software licenses to list. There are 4 major Open Software licenses (and I await the onslaught of edits to extend this list for those I've forgotten):
- OSL 3.0
- New BSD
And many of your favorite open source software products probably use one of those 4 above.
How do I make the choice?
Jeff Atwood has done a great job of comparing the licenses on his Coding Horror blog: http://www.codinghorror.com/blog/2007/04/pick-a-license-any-license.html
There is a 'license chooser' web app available, too: http://three.org/openart/license_chooser/
Phil Haack distills all of this down to the following four types of licenses; I tend to agree with him:
Proprietary - The code is mine! You can’t look at it. You can’t
reverse engineer it. Mine Mine Mine!
GPL - You can do whatever you
want with the code, but if you distribute the code or binaries, you
must make your changes open via the GPL license.
New BSD - Use at your
own risk. Do whatever the hell you want with the code, just keep the
license intact, credit me, and never sue me if the software blows your
foot off. The MIT license is a notable alternative to the New BSD and
is very very similar.
Public Domain - Do whatever you want with the
code. Period. No need to mention me ever again. You can forget I ever
For all intents and purposes it sounds to me like New BSD/MIT is what you're looking for, however, only you can make this decision.
For the record, Magento is AFL 3.0, but used to be OSL 3.0. http://www.magentocommerce.com/license/
Arguably, the most important feature of these licenses is GPL Compatibility. The Free Software Foundation endorses many others on their own site - cited here in this Wiki: http://en.wikipedia.org/wiki/List_of_FSF_approved_software_licenses
You need to make your own choice. No one can take a short question on StackExchange and interpret your individual needs. In general, if you don't want your software shared over public networks, you want to look at OSL 3.0 and its variants.
Once I've chosen a license, how do I apply it?
Include attribution and license notice at the top of all of your files. Include a LICENSE.TXT and a link to a license notice on your own site.