MBSA

MBSA : Microsoft Baseline Security Analyzer
Microsoft Baseline Security Analyzer (MBSA) is an easy-to-use tool designed for the IT professional that helps small and medium-sized businesses determine their security state in accordance with Microsoft security recommendations and offers specific remediation guidance. Built on the Windows Update Agent and Microsoft Update infrastructure, MBSA ensures consistency with other Microsoft management products including Microsoft Update (MU), Windows Server Update Services (WSUS), Systems Management Server (SMS) and Microsoft Operations Manager (MOM). Apparently MBSA on average scans over 3 million computers each week.

SAINT

SAINT : Security Administrator’s Integrated Network Tool
SAINT is another commercial vulnerability assessment tool (like Nessus, ISS Internet Scanner, or Retina). It runs on UNIX and used to be free and open source, but is now a commercial product.

Sara

Sara : Security Auditor’s Research Assistant
SARA is a vulnerability assessment tool that was derived from the infamous SATAN scanner. They try to release updates twice a month and try to leverage other software created by the open source community (such as Nmap and Samba).

X-scan

X-scan : A general scanner for scanning network vulnerabilities
A multi-threaded, plug-in-supported vulnerability scanner. X-Scan includes many features, including full NASL support, detecting service types, remote OS type/version detection, weak user/password pairs, and more. You may be able to find newer versions available here if you can deal with most of the page being written in Chinese.

ISS Internet Scanner

ISS Internet Scanner : Application-level vulnerability assessment
Internet Scanner started off in ’92 as a tiny open source scanner by Christopher Klaus. Now he has grown ISS into a billion-dollar company with a myriad of security products.

Retina

Retina : Commercial vulnerability assessment scanner by eEye
Like Nessus, Retina’s function is to scan all the hosts on a network and report on any vulnerabilities found. It was written by eEye, who are well known for their security research.

GFI LANguard

GFI LANguard : A commercial network security scanner for Windows
GFI LANguard scans IP networks to detect what machines are running. Then it tries to discern the host OS and what applications are running. I also tries to collect Windows machine’s service pack level, missing security patches, wireless access points, USB devices, open shares, open ports, services/applications active on the computer, key registry entries, weak passwords, users and groups, and more. Scan results are saved to an HTML report, which can be customized/queried. It also includes a patch manager which detects and installs missing patches. A free trial version is available, though it only works for up to 30 days.