The standard Ruby distribution contains useful tools along with the interpreter and standard libraries −
These tools help you debug and improve your Ruby programs without spending much effort. This tutorial will give you a very good start with these tools.
RubyGems is a package utility for Ruby, which installs Ruby software packages and keeps them up-to-date.
To help deal with bugs, the standard distribution of Ruby includes a debugger. This is very similar to gdb utility, which can be used to debug complex programs.
irb (Interactive Ruby) was developed by Keiju Ishitsuka. It allows you to enter commands at the prompt and have the interpreter respond as if you were executing a program. irb is useful to experiment with or to explore Ruby.
Ruby profiler helps you to improve the performance of a slow program by finding the bottleneck.
There are other useful tools that don't come bundled with the Ruby standard distribution. However, you do need to install them yourself.
eRuby stands for embedded Ruby. It's a tool that embeds fragments of Ruby code in other files, such as HTML files similar to ASP, JSP and PHP.
When you have a question about the behavior of a certain method, you can invoke ri to read the brief explanation of the method.
For more information on Ruby tool and resources, have a look at Ruby Useful Resources.