Using a shared hosting plan has many advantages and disadvantages. However, a good understanding of these can only be achieved if you know what other websites are being hosted on the same server (IP address).
MY IP Neighbors is great little tool that tells you which other websites are hosted on the same server/IP. Simply enter the URL of a website and a list of all the websites hosted on that IP would be displayed along with the resolved date. Clicking on the Whois link next to any of the listed websites would display detailed whois information from Domain Tools.
You can also set up an email notification so you will get notified every time a new website is added to your server. Another great use of the tool is to check if your dedicated server has been compromised.
MY IP Neighbours is a very useful tool to see what other websites are hosted on the same server. The interface is simple and the tool is super easy to use.