Yougetsignal is an interesting service with set of tools for checking network ports, reverse IP domain check etc.
Port Forwarding Tester: With this you can check your external IP address and detect open ports on your connection. Useful for finding out if your port forwarding is setup correctly or if your applications are blocked by a firewall. The most common ports are already available in the site, just click on any port to see if it is closed or open.
Network Location Tool: This tool displays your network location on a Google Map, with details like IP, domain, country etc.
Visual Trace Route Tool: Visual Trace tool as the name suggests shows visually the path of the internet packets along the way to the destination network address.
Reverse IP Domain Check: With this tool you can check what are the other domains hosted along with a specific domain. It is a good tool some of the services charge users to get this information or ask you to register. If you are on a shared hosting you can check what other domains are hosted along with you, some hosts may contain few hundred sites on the same server. Also see Check DNS and Mail Server Configuration.
Other useful tools include Phone no geo location and domain whois lookup. This site is worth to bookmark, the provided tools are quite useful. Via Makeuseof