One of Yahoo's acquisitions back in September '07 was Zimbra, an open source (MPL) groupware product that's garnered a reputation as a solid alternative to Microsoft Exchange.  Now, with Microsoft prepping a potential buyout of Yahoo, there's real fear in the air that Zimbra may be one of the casualties.

At first the picture doesn't seem so bleak.  Zimbra's open source, so we could just fork it and be done with it.  But there's key components of the commercial edition of Zimbra that are closed source, which many customers depend on, and can't be forked or relicensed as easily.

One of the concerns voiced by existing Zimbra users in an ongoing message thread is what will happen to customers who spent money on the commercial version.  If Microsoft's buyout goes through and it decides to let Zimbra die (or actively kill it), those people may be left twisting in the wind.

Zimbra, meanwhile, continues undaunted with the launch of the 5.0 version of its product.  I especially liked the line: "I can confidently say that the Zimbra movement is bigger than any one company."

Groklaw has its own analysis as well, and one sentence in particular stuck with me: "Now we see what mixed licensing results in. Trying to be [both] FOSS and proprietary is tricky."  Unfortunately, in a world like this, mixed licensing may be one of the more solid ways to get open source to gain traction with the people who can become its biggest and most important advocates.