The Android OS project, for example, opted to release the core Android components under the Apache license, rather than the GNU General Public License (GPL) which is usually popular with open source GNU/Linux software.
Using the Apache license was a strategic move for Google, because the Apache license is less restrictive than the GPL; with the GPL, any software you write that incorporates GPL code must also be released, in its entirety, under the GPL license. Just by using GPL code in your application, your whole application must be made open source under the same terms as the GPL'd code you borrowed for it.
To put this in perspective, let's imaging a hypothetical story in which Adobe decides to add a new image format into Photoshop, and they use some code for this image format which is released under the GPL license. Because Photoshop is using GPL'd code--even though they're using only a tiny bit in comparison to the rest of Photoshop's code--Adobe would be forced to release Photoshop in its entirety under the GPL license; they would have to provide all of its source code to its users, and you could therefore just download it and compile your own Photoshop from source code.
Proprietary software companies like Adobe of course wouldn't like this, so they don't generally like to use GPL-licensed code in their products; the GPL is considered viral because it "infects" the entire application and forces it all to become open source just because it is. The GPL is a "copyleft" license.
Android's code is released under the Apache license instead because, that way, individual vendors can make their own modifications and additions to the base Android code, and add proprietary features to keep an edge over their competition. If their contributions to the Android core was forced to be made open source, as the GPL would require, they would be less inclined to spend time and money developing their new features in the first place, because their competitors could easily just take their code for themselves in their own Android devices.
So what does this all mean for RiveScript?
RiveScript has always been released under the GNU General Public License, which would be great if RiveScript was, itself, a complete software application. It isn't. RiveScript is just a library, a Perl module, and it doesn't do anything until you write an actual Perl application that loads the module.
So if somebody wanted to create and sell a closed source "desktop assistant" type application, with a pretty GUI and an animated face and it could speak to you out loud and understand you when you speak to it out loud, and it simply wanted to use my RiveScript module for the artificial intelligence part... they wouldn't be able to release it as a closed source product. The GPL license governing the RiveScript library would force their entire application to be made open source.
This obviously isn't ideal; and so, usually, libraries are released under the GNU Lesser General Public License, which is an ideal license to be used for software libraries.
Under the LGPL, an application would be allowed to use my RiveScript library and still be, overall, a closed source application. The only restriction would be if they wanted to modify RiveScript itself, to add new features to it or extend its functionality in any way; if they touch my RiveScript module itself, their changes would have to be released to the public as open source. But, it wouldn't touch the rest of their product at all; they could still keep their overall product closed source and sell it if they wanted to.
So, I'm thinking I should relicense RiveScript and maybe see if that will help drive more developers to use it in their projects. The LGPL though isn't particularly ideal for a Perl module though since the license deals a lot with terminology like "linking" which only applies to C/C++ code. But maybe the old tried-and-true Artistic License that Perl itself is released under would do just as well.
I'll work out the details later but expect RiveScript 1.22 to be licensed more openly; or, at the very least, dual-licensed to be used in both open and closed source projects.
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I think Android should be licensed under GPL since it used Linux "kernel" not just some codes.
I find it a bit ironic that you're using "licensed more openly," to mean licensed so that it can be used as closed proprietary software. I disagree with proprietary software's ideals, but you seem to have thought it out well and make some good points. Of course, I think it would be great if proprietary programs had to become free (as in freedom) because they chose to use your library. :)