Censys is described as 'Search engine that allows computer scientists to ask questions about the devices and networks that compose the internet' and is a vulnerability scanner in the network & admin category. There are more than 25 alternatives to Censys, not only websites but also apps for a variety of platforms, including Linux, Windows, Mac and SaaS apps. The best Censys alternative is Metasploit. It's not free, so if you're looking for a free alternative, you could try Metasploit or Shodan. Other great sites and apps similar to Censys are Social-Engineer Toolkit, Whatoblock, ZoomEye and OSINT Researcher.