Licences in Open Source
" The terms 'free' and 'open', as used by the Free Software Foundation and the Open Source Initiative, denote a disagreement over a specific license provision called "copyleft."
'Free' software, defined by the FSF, has a license clause called copyleft. This clause requires that if you distribute modified versions of the software, your version must be governed by the same license as the original. The idea is that the software can be modified but can never become less open - redistributers must grant the exact same rights they themselves enjoyed. The GNU GPL is the paradigmatic example of this license type.
'Open-source' software, as defined by the OSI, requires you to include the source code when distributing the software, and grants rights of modifying and redistributing it. Aside from these terms, it doesn't specify an exact license that redistributers must follow.
The Apache license and the MIT license are two popular examples of this kind.
Generally the 'open' model is considered more business-friendly, while the 'free' model is preferred for civil libertarian purposes - stuff like encryption tools, for example. "
I personally like the BSD-2 or BSD-3 clause.
GPL-2 vs GPL-3
There's some interesting debate in the linux community between GPL-2 and GPL-3 but GPL-3 seems to follow most closely with R. Stallman's vision for the GPL license. That is, if an author wants his software to be usable in perpetuity, then use a copyleft license like GPL-3, not even hardware can lock down access.