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

Question

Most of the code I write is in Ruby, and every once in a while, I make some typo which only gets caught after a while. This is irritating when I have my scripts running long

Answer 1

avdi@lazarus:~$ irb
>> a = 20
=> 20
>> b = 30
=> 30
>> puts c
NameError: undefined local variable or method `c' for main:Object
        from (irb):3
>>

There ya go, the tool is called "IRB". Do I get the bounty?

I'm only half joking. I wrote this second answer to hopefully drive home the point that in Ruby, if you want to know that something is defined or not, you have to run the code.