SAINT

SAINT is a commercial vulnerability assessment tool. Like Nessus, it used to be free and open source but is now a commercial product. Unlike Nexpose, and QualysGuard, SAINT runs on Linux and Mac OS X. In fact, SAINT is one of the few scanner vendors that don't support (run on) Windows at all.

Nipper

Nipper (short for Network Infrastructure Parser, previously known as CiscoParse) audits the security of network devices such as switches, routers, and firewalls. It works by parsing and analyzing device configuration file which the Nipper user must supply. This was an open source tool until its developer (Titania) released a commercial version and tried to hide their old GPL releases.

Secunia PSI

Secunia PSI (Personal Software Inspector) is a free security tool designed to detect vulnerable and out-dated programs and plug-ins that expose your PC to attacks. Attacks exploiting vulnerable programs and plug-ins are rarely blocked by traditional anti-virus programs. Secunia PSI checks only the machine it is running on, while its commercial sibling Secunia CSI (Corporate Software Inspector) scans multiple machines on a network.

Retina

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.

MBSA

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).

QualysGuard

QualysGuard is a popular SaaS (software as a service) vulnerability management offering. It's web-based UI offers network discovery and mapping, asset prioritization, vulnerability assessment reporting and remediation tracking according to business risk. Internal scans are handled by Qualys appliances which communicate back to the cloud-based system.

GFI LanGuard

GFI LanGuard is a network security and vulnerability scanner designed to help with patch management, network and software audits, and vulnerability assessments. The price is based on the number of IP addresses you wish to scan.

Nexpose

Rapid7 Nexpose is a vulnerability scanner which aims to support the entire vulnerability management lifecycle, including discovery, detection, verification, risk classification, impact analysis, reporting and mitigation. It integrates with Rapid7's Metasploit for vulnerability exploitation. It is sold as standalone software, an appliance, virtual machine, or as a managed service or private cloud deployment.

Core Impact

Core Impact isn't cheap (be prepared to spend at least $30,000), but it is widely considered to be the most powerful exploitation tool available. It sports a large, regularly updated database of professional exploits, and can do neat tricks like exploiting one machine and then establishing an encrypted tunnel through that machine to reach and exploit other boxes. Other good options include Metasploit and Canvas.

OpenVAS

OpenVAS is a vulnerability scanner that was forked from the last free version of Nessus after that tool went proprietary in 2005. OpenVAS plugins are still written in the Nessus NASL language. The project seemed dead for a while, but development has restarted.

Nessus

Nessus is best vulnerability scanners, particularly for UNIX systems. It was initially free and open source, but they closed the source code in 2005 and removed the free "Registered Feed" version in 2008. It now costs $1,200 per year, which still beats many of its competitors. A free “Home Feed” is also available, though it is limited and only licensed for home network use.