One of the beautiful things about virtualization is that we can pretty much stop writing software and start writing glues. We no longer need to care about whether software is cross-platformed. We can choose the platform for which we want to develop our products.

I guess all of this sounds too futuristic but I truly believe that one day we will download and install appliances the way we download and install software. Products such as VMWare, VirtualBox and QEMU will be treated no different than Java, .NET, Flash, Adobe AIR and other development platforms. Effectively, we will start thinking in terms of how many CPUs we can handle rather than how many processes although in reality virtual appliances are processes running in the host system. It will all merge and the permutations will become deep and complicated but at the same time this approach may allow us to build self-sustainable systems.

And this is what it is referred to as Software as an Appliance.