People using Ruby generally have a way to install different Ruby versions, manage their packages (or gems), and manage their gem dependencies.
Ruby was created by Yukihiro “Matz” Matsumoto, who remains somewhat of a BDFL, although that is changing recently. As a result, the reference implementation of Ruby is called MRI (Matz' Reference Implementation), and when you hear a Ruby version, it is referring to the release version of MRI.
New major versions of Ruby are traditionally released on Christmas Day. The current major version (25 December 2017) is 2.5. The most popular stable versions are 2.4.4 and 2.3.7 (both released 28 March 2018).
Some platforms have Ruby pre-installed or available as a package. Most rubyists do not use these, or if they do, they only use them to bootstrap another Ruby installer or implementation. Instead rubyists tend to install a Ruby manager to install and switch between many versions of Ruby and their projects' Ruby environments.
The following are the popular Ruby environment managers:
The Ruby ecosystem enjoys many different implementations of Ruby, each with unique strengths and states of compatibility. To be clear, the different implementations are written in different languages, but they are all Ruby. Each implementation has special hooks and extra features, but they all run normal Ruby files well. For instance, JRuby is written in Java, but you do not need to know Java to use it.
Ruby implementations may have their own release version numbers, but they always target a specific version of MRI for compatibility. Many implementations have the ability to enter different modes (for example, 1.8 or 1.9 mode) to specify which MRI version to target.
Most Ruby implementations rely heavily on RubySpec. Ruby has no official specification, so the community has written executable specs in Ruby to test their implementations' compatibility with MRI.
RubyGems is a community-run package manager for Ruby. RubyGems ships with Ruby, so there is no need to download it separately.
Ruby packages are called “gems,” and they can be hosted by the community at RubyGems.org. Each gem contains its source code and some metadata, including things like version, dependencies, author(s), and license(s).
Bundler is a gem dependency resolver. It uses a project’s Gemfile to find dependencies, and then fetches those dependencies' dependencies recursively. It does this until all dependencies are resolved and downloaded, or it will stop if a conflict has been found.
Bundler will raise an error if it finds conflicting dependencies. For example, if gem A requires version 3 or greater of gem Z, but gem B requires version 2, Bundler will notify you of the conflict. This becomes extremely helpful as many gems refer to other gems (which refer to other gems), which can form a large dependency graph to resolve.
Testing is a large part of Ruby culture. Ruby comes with its own Unit-style testing framework called minitest (Or TestUnit for Ruby version 1.8.x). There are many testing libraries with different goals.
The Ruby community takes pride in being an open, diverse, welcoming community. Matz himself is extremely friendly, and the generosity of rubyists on the whole is amazing.
Originally contributed by Jon Smock, and updated by 8 contributor(s).