Few tech observers take them seriously, but they're getting harder to ignore. More companies, including Hewlett-Packard (NYSE: HPQ), are starting to offer Chromebooks -- laptops running Google's (NASDAQ: GOOG) Chrome operating system. This is obviously problematic for Microsoft (NASDAQ: MSFT), as Chrome OS could become yet another threat to Windows.

The problem with Chromebooks
Admittedly, it's a bit disingenuous to characterize Chrome OS as a real operating system -- for the most part, Chromebooks can't run local software. Instead, what they offer is merely a slightly souped-up version of Google's popular Chrome browser. In effect, Chromebooks are merely gateways to the Internet.

But that means that they're cheap -- Acer's 11.6-inch Chromebook costs just $199. They're also lightning fast -- there's no software running in the background to slow the computer down -- and invulnerable to viruses.

For the average user, one who spends their time browsing the Internet, checking Facebook, reading email and doing some light word processing, Chromebooks are ideal. But even among business users, Google's operating system could be an attractive alternative to Microsoft's Windows.

Software is migrating to the cloud
That's because increasingly, companies are relying on cloud-based software. Here, Google's Chromebooks tackle the job quite easily, able to handle the popular cloud-based programs offered by companies like Salesforce. Even AutoCAD, Autodesk's demanding drafting program, is now available as a cloud-based application.

Asus, when announcing that it was going to start making laptops with Google's operating system, characterized Chromebooks as being potentially more popular among government agencies and businesses than consumers.

Asus and Acer aren't the only companies making Chromebooks -- Samsung's $249 model has been the top seller on Amazon since January, and Toshiba and Lenovo have also announced Chromebooks. More recently, struggling Microsoft Windows PC-maker HP has embraced the Chromebook with gusto, releasing its second model earlier this week.

Hewlett-Packard moves away from Microsoft, embraces Google
There are growing signs that Hewlett-Packard is becoming uneasy with Microsoft. During Hewlett-Packard's analyst meeting on Wednesday, CEO Meg Whitman characterized Microsoft as a competitor. Although Microsoft and Hewlett-Packard remain major partners for the time being, that relationship is starting to look fragile.

Microsoft's failure to deliver a solid product in Windows 8 may be partially responsible for the declines seen in PC sales, a major factor in HP's ongoing struggles. More important is Microsoft's decision to begin making its own hardware, like the Surface and Surface Pro, which competes directly with HP's own Windows 8-based tablets. Microsoft even loaned Michael Dell $2 billion to help him take his company -- one of HP's biggest competitors -- private.

It's little wonder, then, that HP has been working more closely with Google. HP has released several Android-based tablets, and has been helping Google sell its Google Apps to small businesses -- a competitor to Microsoft's Office.

That partnership extends to Chromebooks. The HP Chromebook 11, released earlier this week, follows the HP Chromebook 14, announced last month. Still, this is a relatively new direction for HP -- it released its first Chromebook just last February.

As HP's relationship with Microsoft grows more uncertain, the PC OEM may put more emphasis on Google's operating system

It isn't just mobile devices that threaten the Microsoft Windows PC
While most observers agree that mobile devices, including smartphones and tablets, are weakening the demand for traditional PCs, Google's Chromebooks also loom as a potential threat. Although their market share may still be relatively tiny, it's one PC sector that's actually seeing growth.

Moreover, Microsoft, in its quest to break into mobile, has alienated some of its hardware partners, including HP, who have begun to push Google's Chromebooks as an alternative to traditional PCs running Microsoft's operating system.

For now, Chromebooks may remain an oddity, but as more of them are released, and more software migrates to the cloud, they could become a real force in the world of personal computing. Certainly, they shouldn't be underestimated.

The rise of Chrome OS is just a tiny part of the Google story
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Sam Mattera has no position in any stocks mentioned. The Motley Fool recommends Google and Salesforce.com. The Motley Fool owns shares of Google and Microsoft. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.