Matt Mullenweg had to make a pretty clear statement that WordPress is Open Source in response to some sniping from MT.
I already left a comment in support of Matt, and he tossed it back my way:
Thanks Boris, I think the way Drupal and WordPress have co-existed is a great model to follow despite a few distractions along the way, and your role in facilitating that as an ambassador has been crucial. It’s rare for code for one project to be directly applicable to another, but ideas and values are contagious — in the good Isley Brothers way.
I know how this can be. We flirted with dual licensing around Bryght's mass hosting system, Hostmaster. In hindsight, it probably delayed development by 2 years. Now hosted on Drupal.org, Hostmaster has a couple of more developers buying in and it feels like we're developing some momentum.
We made a Bryght "install profile" -- a bundle of code and configuration and a little custom module for doing some cool stuff with CSS overrides. From day one, it's been hosted on our public SVN repository, and includes the original CVS tags from Drupal.org itself.
It was amusing to watch that MT4 actually had as a feature that other systems had adopted their templating system -- namely a single contributed module in Drupal that can support MT themes for bloggy sites.
Basically, sniping other open projects isn't cool. In the first meetings that the Drupal community ever had as a group, in Antwerp and Amsterdam, we had Joomla community members and senior devs. It was so fun playing with the Joomla guys and matching t-shirts and groups shots with Rasmus at OSCMS 2007. Amy Stephens +1 -- check out Open Source Community.
The "enemy" here is proprietary systems (and those really are quotes around enemy, as I recall having a great discussion with a proprietary Java based system developer this morning at CCI2008). They are not good for business, they are not good for communities, and they are not good for the growth of this interlinked web of data that is becoming truly useful.
I ran a couple of not really that successful because they were TOO Drupal heavy "Open Source CMS Summits". I'd love to do more of them, because we have so much to learn from each other, but we are all so focused on growing our own communities, each bit of *friendly* rivalry pushing the others to get better. Like the Isley Brothers :P