Free Windows security scanners

Free network vulnerability scanners:

http://www.networkworld.com/article/2176429/security/6-free-network-vulnerability-scanners.html

Free tools from Tripwire and Rapid7:

http://www.tripwire.com/free-tools/

http://www.rapid7.com/resources/free-tools.jsp

Microsoft Baseline Security Analyzer:

https://www.microsoft.com/en-us/download/details.aspx?id=7558