Reinhold Weber has posted his lists of some of the similarities and differences between Ruby and PHP:

If you are a PHP developer chances are you have heard some of the buzz on Ruby on Rails, an open source web framework for rapid application development. [...] These are similarities and differences of Ruby compared to PHP. If you know PHP, this should give you a good and quick insight in what Ruby is all about and how it compares to PHP.

Some of the similarities include the dynamic typing, class scoping, heredoc abilities and current object references. Differences include syntax differences, method calling, naming conditions and Ruby's lack of interface/abstract classes.

From the RefreshinglyBlue blog, there's a new post that makes a comparison between two of the most popular web scripting languages - PHP and Ruby - on a practical, basic level.

There are rather significant syntactical differences between PHP and Ruby. For example PHP requires semicolons at the end of lines and generally requires curly brackets to enclose blocks of code. Ruby, on the other hand, uses newline characters to denote the end of a line of code...

The post goes through other differences like: value return methods, function/method naming, similarities between them, frameworks, namespaces, documentation and hosting options.