Nessus Remote Security Scanner
Recently went closed source, but is still essentially free. Works with a client- server framework.
Nessus is the worlds most popular vulnerability scanner used in over 75,000 organizations world-wide. Many of the worlds largest organizations are realizing significant cost savings by using Nessus to audit business-critical enterprise devices and applications.
Visite Nessus Here – http://www.nessus.org