GPL & Open Source Software

Study Licenses such as GPL, MIT, etc.
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Basic
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The "copyleft effect" can take different forms.  
Strict copyleft licenses demand that any changes be released as open source software,
whereas limited copyleft licenses only require this in certain cases.  For example, the
Mozilla Public License (MPL) only requires that changes to existing files have to be released,
whereas added files can be licensed in any way. The Lesser General Public License (LGPL) for
program libraries only requires that changes to the library itself are subject to the LGPL.
The program accessing the library can have any type of license.

Commercial Open Source Software
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May open source software be commercial?
Yes!  The freedom of use granted by open-source licenses also allows open source software
to be sold or leased.  It is therefore a widespread misconception that open source software
and commercial software are contrasting opposites. Open source software can be free,
but not necessarily.

However, license fees may not be charged for open source software.  License fees are a
reimbursement for being granted rights of use.  For this reason, remuneration can be
charged for the sale of software (that is, the data carrier with the software or the
option to download the software), but not for the license.  Practically speaking, the
difference lies in a three-person relationship.  The licensee may copy and distribute
the copies of the open source software that was either purchased or acquired for free
without having to pay the licensor anything.  The licensor cannot make the use of the
software dependent on a fee.
[My opinion: the vendor / licensor must find a way so that even if the software is copied
and distributed freely, users still have to pay the vendor to get a good user experience.
It's like free online games. You can acquire a free acount and play the game, however, if
you want to have the rule-in-the-game feeling, you've got to pay.]



Question
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1) Why is some particular license created?
   In other words, what do we need these licenses for?
"Copyleft licenses" require licensee to license specific developments (if they are not restricted
to internal use) to anyone under the original license. This ensures that everyone who profits
from open-source software will offer their developments to the developer community.

2) What's the key difference between GPLv2 and GPLv3 licenses?
The GPLv3 license has more restrictions. If a program includes code or library that has a GPLv3
license, then the entire program becomes GPLv3.

3) open source code != open source software
open source software
= open source code
+ free redistribution
+ derived works
+ integrity of the author's source code
+ no discrimination against persons or groups
+ no discrimination against fields of endeavor
+ distribution of license
+ license must not be specific to product
+ license must not restrict other software
+ license must be technology-neutral


References
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http://opensource.org/docs/osd
(The Open Source Definition)

http://www.ifross.org/en/faq-frequently-asked-questions
(Open Source FAQ)