Best base license to pick?

[Alex Bligh]

I am working with a company that is investigating putting a large software
project into an open source environment, hopefully under a license approved
by OSI.

The route we are currently exploring is, I believe, conformant to v1.9 of
the Open Source Definition. Essentially, they want to license "their" code
(by which I mean that which they own or can freely sublicense) under
something similar to the GPL (requiring those making derivative works to
make the source code available etc.), whilst still retaining the right to
use the contributed code in a commercial version of their own (no problem
with GPL so far, as far as I can see, as it's their code to license - you
don't give up your own rights by licensing using GPL).

However, the current thought is to do something slightly different:

Firstly, they want to (inter alia) ensure file format and library interface
compatibility between different version, and to know what code is theirs
(i.e. either written by them, or with IPR assigned to them or licensed to
them under a separate contribution agreement) so they don't end up
accidentally putting someone else's GPL code into their commercial version;
they also want to retain what I think the Artistic License refers to as
artistic control of the development process if possible. It currently seems
that the best way to do this for them is the caveat at the bottom of (4) of
the Open Source Definition:
	Accordingly, an open-source license must guarantee that source be
	readily available, but may require that it be distributed as
	pristine base sources plus patches. In this way, "unofficial"
	changes can be made available but readily distinguished from the
	base source.
IE they want to ensure that anyone distributing executables of derived
works MUST make source available, and anyone who distributes source
of derived works (whether or not with executables) MUST do so in the
form of the pristine tree plus diffs.

Secondly, they want to take a modern approach to patents, minimizing risk
of patent litigation (and have no problem allowing any patents of their own
to be used by derived works etc.).

Thirdly, they are conscious of the problems of license proliferation, so
would be keen to use something existing if possible, and ideally something
well known and with credibility. Failing that, they'd like to base theirs
on such a license, and make only minimal changes.

Are their any particular OSI approved licenses they should be looking at to
start off with?

I'm hoping this a fair venue for this question as the intent is to
get OSI approval if it's a new license - if not, pointers to a suitable
mailing list would be gratefully received.

Alex