Firstly, PHP was built to be a server language, first and foremost. That's one of the primary reasons it's not usually used for anything other than web applications - it's not designed for it and therefore can't match up to the requirements of, say, a scripted desktop application.
Ruby was designed as a general-purpose scripting language, and thus has a wide support for a number of different applications. It has been used across the board for everything from web applications, to web servers themselves, to intelligent graphing libraries, to picture recognition engines, to threaded database servers, to low-level system utilities. It has a wide spectrum of use throughout computing.
Rails has most certainly boosted the popularity of Ruby by a huge amount, brought it up into the forefront of scripting languages, spawning 40+ books, 18 conferences, distribution with nearly all the major operating systems and 7 different implementations to boot!
To begin with, all of Rails' internals are written in Ruby itself, but all of the Rubygems, libraries, snippets or anything else that is used by Rails developers is written in Ruby too, and is most likely built to work outside of the Rails stack.
Having said that, the popular web framework is not the reason why Ruby is popular. Sure, it has helped bring much-needed attention to the language, but it's not the reason why people use it day to day. It's used for everything from web applications to desktop GUI applications because of it's simple, elegant syntax, it's clean, sensible and complete standard library, it's wide ecosystem of community code, support and toolchains.
Ruby is used because it rocks.
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