Idea Community Edition Ruby Plugin
Check this if you buy it by yourself: In fact, you should see things like this: - Community Edition is the Java IDE. It has support for most of JVM languages, Android but doesn't not offer support of web technologies (like framework, DB tools).
You have access to all community plugins (D, GO, Rust.) freely. There is also a PyCharm Community Edition which offer the same things but for Python. Ultimate Edition is litteraly the ultimate version of IDEA, with support of ALL languages officially supported by JetBrains (HTML/CSS/JS + languages based on them, PHP, Ruby, full Python support.).
Idea Community Edition
It's the most complete version but usually, you don't need it if you don't do web dev in Java or don't need to work with multiple languages supported by smaller IDE. Other JetBrains IDE (PHPStorm, RubyMine.). Those IDE support HTML/CSS/JS + one language (PHP, Ruby or Python). They are cheaper, offer access to all third party plugins but doesn't support Java development. They are developed by a dedicated team and offer really good support for targeted language.
2nd puc notes. So yes IDEA Ultimate is expensive but many people just need a 'smaller' IDE.