IPlocals 
Posted on March 16, 2009
Reverse IP Tool
IPlocals is a free reverse IP tool will will allow you to check what sites are hosting on your server/hosting package.
This is particularly useful with shared hosting where you can discover if your hosting is oversold.
Ignace Rodríguez / @micronauta March 16, 2009
In my opinion totally useless. You see, a nice big server farm can be (and actually should be) clustered behind load balancing hardware, so any number of web servers can be hidden behind a single IP address, making the information provided by a reverse IP address lookup totally meaningless. Sorry.