Yang!

The Nessus vulnerability scanner is the world-leader in active scanners, featuring high-speed discovery, configuration auditing, asset profiling, sensitive data discovery and vulnerability analysis of your security posture. Nessus scanners can be distributed throughout an entire enterprise, inside DMZs and across physically separate networks.

Nikto is an Open Source (GPL) web server scanner which performs comprehensive tests against web servers for multiple items, including over 6400 potentially dangerous files/CGIs, checks for outdated versions of over 1000 servers, and version specific problems on over 270 servers.

Snort® is an open source network intrusion prevention and detection system (IDS/IPS) developed by Sourcefire. Combining the benefits of signature, protocol, and anomaly-based inspection, Snort is the most widely deployed IDS/IPS technology worldwide. With millions of downloads and nearly 400,000 registered users, Snort has become the de facto standard for IPS.

A fully automated, active web application security reconnaissance tool. Key features: High speed: pure C code, highly optimized HTTP handling, minimal CPU footprint - easily achieving 2000 requests per second with responsive targets. Ease of use: heuristics to support a variety of quirky web frameworks and mixed-technology sites, with automatic learning capabilities, on-the-fly wordlist creation, and form autocompletion.

Network Hotfix Scanner is a free advanced hotfix check utility that scans network computers for missing hotfixes and patches, and helps you download and install them. NetHotfixScanner gives you a quick look at the hotfixes and patches installed or missed on any remote computer in your corporate network, it tells you by colored icons specific security bulletin rating ( critical, important, moderate ), title, description and bulletin URL. The tool is designed with a user-friendly interface and is easy to use. »

Intruder is a proactive security monitoring platform for internet-facing systems.