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-testing 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
expression 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/