Nexpose is described as 'Find all the vulnerabilities' and is an app in the Network & Admin category. There are more than 10 alternatives to Nexpose for a variety of platforms, including Linux, Windows, Mac, Online / Web-based and Self-Hosted solutions. The best alternative is Metasploit. It's not free, so if you're looking for a free alternative, you could try Shodan or OpenVAS. Other great apps like Nexpose are Nessus (Paid), Censys (Freemium, Open Source), Armitage (Free, Open Source) and Social-Engineer Toolkit (Free, Open Source).
Shodan is a search engine that lets you find specific computers (routers, servers, etc.) using a variety of filters. Some have also described it as a public port scan directory or a search engine of banners.
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 vs Nexpose opinions
pros, cons and recent comments
very similar feature set, and not bloated with other functionality
The Social-Engineer Toolkit is an open source penetration testing framework designed for social engineering. SET has a number of custom attack vectors that allow you to make a believable attack quickly.