The following is my personal interpretation.

MoinMoin's current license is "GNU GPL v2 or later"

MoinMoin's license statement is here: http://moinmo.in/GPL

"The MoinMoin code is licensed under the GPL v2 or (at the user's option) any later version (except some 3rd party modules we use that are licensed under other Free Software licenses compatible with the GPL)."

in moin1.9's README: "This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version."

and in moin2's README.txt: "All rights reserved, MoinMoin is licensed under the GNU GPL v2 or later, see docs/licenses/COPYING for details."

So, I interpret that to mean that MoinMoin is licensed "GPL v2 or any later version".

what that means: http://www.gnu.org/licenses/gpl.html#section14

"you have the option of following the terms and conditions either of that numbered version or of any later version published by the Free Software Foundation."

GPL version 3 is known to be compatible with the Apache License version 2.0

The GPL v3 and the Apache 2.0 license are compatible in the sense that GPL v3 may fully use Apache 2.0 modules.

GNU says Apache 2.0 and GPL v2 are not compatible, but GPL v3 is: http://www.gnu.org/licenses/license-list.html#apache2

Apache agrees and provides more detail, particularly that GPL v3 code may make use of Apache 2.0 code freely: http://www.apache.org/licenses/GPL-compatibility.html

Some thoughtful advice on exactly how to incorporate Apache 2.0 into a GPL v3 project: http://www.softwarefreedom.org/resources/2007/gpl-non-gpl-collaboration.html

We can upgrade MoinMoin to GPL v3

We are free to upgrade to GPL v3 explicitly. GNU also tells how to "upgrade" to GPL v3, and I believe there is no impediment to MoinMoin doing so: http://www.gnu.org/licenses/gpl-faq.html#v3HowToUpgrade

but we don't have to upgrade explicitly if we don't want to

GNU explains: "However, if code is released under GPL “version 2 or later,” that is compatible with GPLv3, because GPLv3 is one of the options it permits." -- http://www.gnu.org/licenses/gpl-faq.html#v2v3Compatibility

According to the chart at http://www.gnu.org/licenses/gpl-faq.html#AllCompatibility , the only exception is if we want to take code from, or link to, other GPLv3 or LGPLv3 software, in which case we must first place the v3 licenses explicitly in the project.

other GPL v3 conversions are going well: http://blogs.fsfe.org/ciaran/?p=98

Other notes:

• for clarity, I think we should upgrade to "GPL v3 or any later version" explicitly.
• might be good to take a careful look at 1.9/docs/licenses/werkzeug/LICENSE and 1.9/docs/licenses/pygments/LICENSE , though.

• some other, lengthy, perhaps not directly related reading: http://www.dwheeler.com/essays/gpl-compatible.html

• Why are GPL v2 and Apache 2.0 not compatible? see http://www.gnu.org/licenses/gpl-faq.html#GPLAndPlugins although it does say "If the program dynamically links plug-ins, but the communication between them is limited to invoking the ‘main’ function of the plug-in with some options and waiting for it to return, that is a borderline case." See also the GPL advice on "interpreters": http://www.gnu.org/licenses/gpl-faq.html#InterpreterIncompat

• Celebrating the compatibility with GPL v3, Apache foundation says it *wants* GPL apps to use their code: http://www.informationweek.com/blog/main/archives/2007/07/apache_foundati.html

• GPL advice on "templates": http://www.gnu.org/licenses/gpl-faq.html#WMS