Google Trend is a keyword comparison tool. Previously it was just used to compare the trend of search keywords but today another feature is introduced by Google, which is Google Trend for Website.
Google Trend for Website can be used to track the popularity of a particular website or you can also compare the Statistics of your site with your competitor’s site.

Here some of the Google Trend for Website features:
1. Compare traffic with up to 5 websites at one time.
2. Keywords which driving traffic to given website
3. View data for a specific country.
4. Related Websites

Previously Alexa ranking was the most popular for comparing websites traffic. However, some users have flagged Alexa data as erroneous.
Google Trend for Website is available for websites worldwide and it really going to help webmasters regarding SEO and comparing their sites with their rivals.