Where can I find an actively developed lint tool for Ruby?

• ruby -c myfile.rb will check for correct Ruby syntax.
• Reek checks Ruby code for common code smells.
• Roodi checks Ruby code for common object-oriented design issues.
• Flog can warn you about unusually complex code.

[Plug] If your project is in a public Github repository, Caliper can run the latter three tools and others on your code every time you commit. (Disclaimer: I work on Caliper)