[om-list] Re: GPL vs. LGPL

[Mark Butler]

Tom,

  The LGPL (Lesser GPL) does not have viral properties like the GPL
does.  You can link LGPL modules to GPL and proprietary modules - that
is why I recommend it in this case. 

A real world example is the GNU C Library (glibc) - if is was not
LGPL, no one (e.g. Oracle) would be able to compile and distribute
proprietary software with the GNU C compiler (gcc).  Most critical
open source infrastructure libraries are LGPL for this very reason.

However, due to the ability for companies to license their *own* code
under looser terms to paying customers, the GPL can actually protect
commercial interests better than the LGPL / MPL. Trolltech has
alternate for their very nice Qt toolkit - normally GPL, proprietary
for paying customers - which forces anyone writing a closed source
product (except themselves, of course) to pay for a license.  Anyone
writing a true GPL product can use it for free.  If Qt were LGPL, most
of their current license revenue would dry up, because most commercial
customers do not really need $1000/year of technical support for a C++
class framework. On the other hand, if it were LGPL, it would probably
dominate the proprietary Unix software world in a matter of months.

The only real reason to combine licenses is to overcome unusual legal
technicalities (e.g. choice of venue) that keep many open source
software licenses from being compatible with the GPL.  Since licensing
code under the GPL is more restrictive than any of the other true open
source licenses, this type of multiple license has little real effect
other than making it possible to use such software in GPL projects.
Since the GPL dominates the free software world, this makes life a lot
easier.  

- Mark