I found a tool to understand the domain that hosts a seridor. It is useful to know, for example, how congested is a shared hosting. Until now there were such tools but they were all charges.

http://www.yougetsignal.com/tools/web-sites-on-web-server/

On the Web can read: "This tool takes the IP web server that is hosting the domain and search other sites hosted on the same server. The information is drawn from results of search tools, which is not guaranteed to be complete information. Knowing that a server hosting other sites is important for both SEO and web filtering, particularly for those servers that are hosted on shared hosting plans "