In irb, you can type the name of an object followed by a dot, then hit tab twice. This will show you all of the methods available on that object.
I’ve heard many times that almost everything is an object in Ruby. So far, everything I’ve encountered seems to be an object, so I went searching to find out what isn’t. My loyal readers (i.e., coworkers) will be happy to know that a post by David Black on the RubyLearning blog was the first result: Almost everything is an object (and everything is almost an object!)