Censys is described as 'search engine that enables researchers to ask questions about the hosts and networks that compose the Internet' and is an website in the Online Services category. There are more than 10 alternatives to Censys, not only websites but also apps for a variety of platforms, including Linux, Windows, Mac 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 Armitage. Other great sites and apps similar to Censys are Social-Engineer Toolkit (Free, Open Source), ZoomEye (Freemium), Exploit Pack (Free, Open Source) and Cobalt Strike (Paid).
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 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.
Vega is a free and open source scanner and testing platform to test the security of web applications. Vega can help you find and validate SQL Injection, Cross-Site Scripting (XSS), inadvertently disclosed sensitive information, and other vulnerabilities.
Immunity's CANVAS makes available hundreds of exploits, an automated exploitation system, and a comprehensive, reliable exploit development framework to penetration testers and security professionals worldwide.