Open Source Licenses

The best place to visit for more information on licenses would be the Open Source Initiative (OSI) at www.opensource.org/docs/definition.php The last time I checked, OSI has certified about 50 different licenses as being conformant with its concept of open source. So there's plenty of choice, but I will mention 3 most popular ones to you here. In any case it probably makes sense to research these a little more on your own since you have the best idea of how strict a licence you are after.

1- GNU General Public License (GPL)
The most known os license, (find the authoritative version at www.gnu.org/copyleft/gpl.html)
It is probably one of the strongest (and notorious) os licenses, it has a section 2b in the license that makes GPL a viral license. That means that if anyone likes your code and uses that code, they have to make their entire software GPL licensed too. The GPL restricts the people that receive your code but not you. In fact you can change the licence for specific people or versions to a more commercial license at any time. However people that already downloaded/agreed to your GPL licensed code version can distribute it under the GPL as long as they like.

2- BSD License, a Berkeley license (www.freebsd.org) used in first edition of Unix, you probably know that already :-). Not as strict to code users as GPL is, for example microsoft is known to have used parts of UNixes networking code in its commercial version of windows.

3-Mozzila Public License (MPL) (www.mozilla.org/MPL) more complex and more loaded with legalese than the GPL, yet it is largerly compatible with GPL. There's one major difference thought. The GPL forbids combining GPL code with proprietary code in a larger piece of work, whereas the MPL expressly allows this. My understanding is that MPL somewhat occupies the middle ground between GPL and BSD licenses.

Funny thing is actually, Microsoft doesn't like open source software :-), they critisize various aspects about os, and therefore they came-up with their own initiative which they called Shared-Source Licenses (see http://www.microsoft.com/resources/sharedsource/default.mspx for more info)

Finally, I'd love to hear various experiences with open source licensing you might have had. You can either comment or email me directly (note: your comment will first go for approval - apologies, but this is necessary due to spam).