A simple DNS server that returns IP addresses on demand.
For testing? Or if you ever find some very bad network access controls that rely on resolving an hostname using dns.
$ nslookup 127-0-0-1.echodns.werebug.com 192.168.1.193
Server: 192.168.1.193
Address: 192.168.1.193#53
Name: 127-0-0-1.echodns.werebug.com
Address: 127.0.0.1
Name: 127-0-0-1.echodns.werebug.com
Address: 127.0.0.1
$ nslookup 0a0a3520.echodns.werebug.com 192.168.1.193
Server: 192.168.1.193
Address: 192.168.1.193#53
Name: 0a0a3520.echodns.werebug.com
Address: 10.10.53.32
Name: 0a0a3520.echodns.werebug.com
Address: 10.10.53.32