As the official Google blog says:
Meet Google Sites, the newest addition to the Google Apps product suite. It was designed to allow you to easily create a network of sites and share them with whomever you choose. Google Sites lets you pull together information from across Google Apps by embedding documents, spreadsheets, presentations, videos, and calendars in your sites. Of course, we also harness the power of Google search technology so your search results are always fast and relevant.Google Sites is the reborn technology from acquisition JotSpot and it's interesting enough in itself, but what's beginning to make Google far more indispensable to Internet users than just a search engine is the the whole Google Apps suite. The integration of the Google Apps suite; its strengths in collaboration among teams, organizations and even everyone; the continual improvements such as the web form recently make them business worthy tools.
And, oh yes, there's the price, free to not much depending on features/level of service desired.
Venture Beat says:
Most significantly, it's the latest move by Google to entice you to transition to Google's "cloud," its collection of servers that lets you store and manipulate your data cheaply. It's a continued challenge to Microsoft's grip on office applications: Indeed, Microsoft's effort to buy Yahoo is also seen by some as an effort by that giant to acquire online customers who will one day use its own cloud, to fend off Google.For me, use of this cloud has already become indispensable in the way I want to work, from various locations, from various computers. with the work at hand always accessible. If search was the killer app of Google's first generation; I think replacing Microsoft Office is the killer app of Google's second generation.
There's more about its features and how to create a Google Site here.
And for anyone with a domain name, Google Apps for your domain is a no-brainer.