What Will An OS Be In A Post-Windows World?

It's not like Microsoft is going to be disappearing any time soon, especially with the success of the Windows 7 beta, but its death grip on the PC industry is being eroded on multiple fronts and it's a good exercise to imagine what it might be like if MS were to take the French leave. It's important to note that the question of what happens after Microsoft doesn't need to mean "what would happen if Microsoft left the picture entirely." Mostly because that's not going to happen: they'll be a part of the post-Microsoft world too, because "Microsoft" is more than a company, it's a way of thinking about computing.