Re: Is it possible to write GPL-Modules for closed-source Software?

[Alfred M. Szmidt]

   Also relevant is that I'm going to use GPL-code from other people
   in my modules.

The following will be relevant to you:

|   2. You may modify your copy or copies of the Program or any
|      portion of it, thus forming a work based on the Program, and
|      copy and distribute such modifications or work under the terms
|      of Section 1 above, provided that you also meet all of these
|      conditions:
|
| [...]
|
|        b. You must cause any work that you distribute or publish,
|           that in whole or in part contains or is derived from the
|           Program or any part thereof, to be licensed as a whole at
|           no charge to all third parties under the terms of this
|           License.


How the copyright holder licenses his work work is up to him, he could
distribute GPL + non-free bits.  The problem is that third parties
(i.e. anyone but the copyright holder) could be sued by the copyright
holder for copyright infrigment if they distribute modified versions
of the work that include the non-free bits; the copyright holder won't
be silly enough to sue himself.

Since you intended to include GPL licensed code from others, you must
obey the license for those works, which means that you cannot use or
link non-free licensed code into your program, as per section 2(b) of
the GNU GPL version 2.

   But do not misunderstand me, I would appreciate your advice, if you
   can give useful answers to my questions.

He can't.  Sadly.

Cheers!