In the first post in this series, I talked about how open-source operating systems were one of a galaxy of three major and complementary forces.  The second, and in some ways more important force, is open-source applications.

One problem that comes right up is what you define as an "application."  You could describe a Linux-based appliance that runs in a 1U rackspace module (or in a virtual machine) as an application, and you wouldn't be far from the truth.  Maybe less so a live distro running as a firewall/router, but there's little question this particular water can be muddied freely.

For the sake of this discussion, though, I'll use the most broadly accepted definition of "application": something you run on top of your OS and deal with directly.  Firefox is a great example: millions of people use it, and it's about as successful an open-source project as you could name.

Since installing an application on an existing system is a lot easier than changing the entire OS, most people sooner adapt open-source applications than they do an open-source OS.  The apps are, if you ask me, the most influential and critical part of open source right now, not OSes, simply because most anyone can pick them up and run with them regardless of what platform they're using.  The size of the slice that Firefox carved out of the browser market pie ought to be the most obvious proof of that.

Granted, it's easy to pop in a Linux live CD, or even run another OS from a virtual-machine system (if you have the memory for it).  But by and large, it's the applications that people work with and deal with most.  The OS is a wrapper, or a "rack", to use the analogy I quoted in my last post.  For people who are just getting work done, the OS isn't the most important thing, and it shouldn't be.

The open-ness of an application also means it can generate its own demand.  A closed-source application can be ported to other platforms if there's demand for it -- and sometimes even if there really isn't -- but an open-source application tends to both generate and satisfy its own demand on multiple platforms.

(Another joking way I've described how open-source apps work is that they're the gateway drug to a full-blown open-source addiction.  Get started with the apps, and you can get hooked with the OS as well at your leisure -- or you can just remain a casual user, if that's more convenient.)

But under the applications and the operating systems (even if the two are eventually sort of becoming the same thing, which I'll talk about another time), there's something even more important, more all-encompassing and critical to the end user: open standards, which includes everything from Internet RFCs to document types.  That will be the subject of the third part of this series.