Doscan is a tool to quickly scan your network for machines listening on a 
TCP port, opening thousands of TCP connections in parallel.
Features
      High scanning rate: five to ten minutes per 100,000 addresses (which 
are sparsely populated with hosts), with rather conservative timeouts.
      Load distribution: doscan scans the addresses in a seemingly random 
order. If your scan host is connected to a central router, this ensures 
that the load is distributed across your network, and you are 
stress-tesing just a single router, and not your edge devices.
      Low memory consumption: memory usage is proportional to the number 
of hosts which have responded so far, and to the number of parallel 
connections. The total number of addresses does not influence memory usage 
in any way.
      Can collect responses: doscan optionally records data which is sent 
by the hosts which are being scanned. You can even specify a regular 
expresson to extract part of a server banner, and a message to send to 
trigger a response (great for determining HTTP server versions).
      Extensibility: It is possible to add special handlers for TCP-based 
protocols, using a straightforward interface.
      It supports scanning the vulnerable Microsoft DCOM implementation.

WWW: http://www.enyo.de/fw/software/doscan/

Janos Mohacsi <janos.mohacsi@bsd.hu>