A Swiss Army Knife to networking.
Tools for webmasters and developers:
Benchmarks and informations about servers, routing, IP-Stacks, encryption, security, nameservers and domains.
Tools for powerusers:
For powerusers ServerSniff.net offers a bit of IPv6-intelligence (try it!) and simply a lot of information about servers, ssl-encryption, domains etc. pp.
ServerSniff.net gathers only public information about servers and networks from publicly available sources or from asking the servers directly.
Serversniff is currently undergoing some rewrite.