As netbook mania (and sales) took off in 2008, it looked like Linux had a chance to be the netbook OS of choice. That is, until Microsoft brought XP out of retirement just for netbooks to use. Now, most netbooks run Windows, and it's likely to stay that way for a while. Still, there are two companies that might pose a threat to Microsoft in the netbook category: Apple and Google.Let's start with Apple. It doesn't have a netbook yet, and some people think Apple just won't get into this low-end territory. And no, the iPhone is not a netbook. Netbooks have big screens and keyboards, like a notebook. Neither is the MacBook Air; at $900, it's not anywhere close to a competitive netbook price range.

If and when Apple delivers a netbook, two things seem certain: It will be elegant, and it will be expensive. Unlike the iPod and iPhone situation, Apple won't be entering the market with a unique product. The iPod defined its category, and the iPhone introduced the first decent phone-based browser. This time, Apple is up against established players such as Acer, Asus, Dell, and Hewlett-Packard. Apple might grab a chunk of this market, but it's unlikely it will dominate it.

Google, on the other hand, could cause Microsoft some trouble. In the same way that Android on phones threatens Windows Mobile, Android on netbooks threatens Windows XP -- and whatever Microsoft designs to follow it. Google might, for example, put its Android operating system and apps store on a netbook.

Android gets high marks for its browsing platform, as does Apple. Microsoft's mobile platform in general, and Internet Explorer in particular, venture into "utter fail" territory. While Internet Explorer on PCs is verging on version 8, Windows Mobile is still saddled with an archaic deviant of IE6. Microsoft just hasn't put in the effort to keep its mobile platform current.

What are the chances that Google could venture into netbook territory? Pretty high. If that article is right, there don't seem to be a lot of technical hurdles. It's more a question of whether Google sees an opportunity in the market. It's not just an opportunity, it's a perfect fit. A tiny and inexpensive netbook is the perfect platform for Google's cloud-based services.

Still, it's hard to count Microsoft out. The company has to retire its XP netbook offering when Windows 7 comes out. Can Windows 7 tame Vista's bloat in order to be an effective netbook OS?