This aims to be a summary of GPL licenses in plain, simple English

GNU General Public Licence, version 2. (GPLv2)

The GPL protects your four freedoms:

• Obtain and run the program for any purpose
• Get a copy of the source code
• Modify the source code
• Re-distribute the modified source code

Restrictions:

If you want to re-distribute GPLv2 software, you must:

• provide access to the source code
• license derived work under GPLv2 (or later?) licence

Otherwise, you don't need to make source code available if you are not distributing any part of it. I.E. you either distribute both the binary and source code, or distribute nothing.

GNU General Public License, version 3. (GPLv3)

Please help complete this part. See here

This is how I understand it so far:

• It is still a draft (Discussion Draft 2 of Version 3, 27 July 2006)
• It does not allow DRM. (details needed.)

quote

Some computers are designed to deny users access to install or run modified versions
of the software inside them. This is fundamentally incompatible
with the purpose of the GPL, which is to protect users’ freedom; to
change the software. Therefore, the GPL ensures that the
software it covers will not be restricted in
this way.

• It aims to be more effective against software patents. (details needed.)

The GPL assures that any patent cannot be used to render the program non-free

• The linux kernel developers may not adopt v3 anytime soon and continue to use v2.

  • quote

    The kernel developers see the DRM clauses, which attempt to restrict developers from imposing usage rights on GPL-licensed software, as something that impedes freedom. 
    
    "While we find the use of DRM by media companies in their attempts to reach into user-owned devices to control content deeply disturbing, our belief in the essential freedoms of section 3 forbids us from ever accepting any license which contains end use restrictions," the position paper states. 
    
    "The existence of DRM abuse is no excuse for curtailing freedoms." 

  • "As drafted, this currently looks like it would potentially jeopardise the entire patent portfolio of a company simply by the act of placing a GPLv3 licensed programme on their website," the position paper states. 
    
    "Since the Linux software ecosystem relies on these type of contributions from companies who have lawyers who will take the broadest possible interpretation when assessing liability, we find this clause unacceptable because of the chilling effect it will have on the necessary corporate input to our innovation stream." 

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