Top Level Namespace

Modules:

AbstractController, ActionCable, ActionController, ActionDispatch, ActionMailbox, ActionMailer, ActionPack, ActionText, ActionView, ActiveJob, ActiveModel, ActiveRecord, ActiveStorage, ActiveSupport, Arel, DateAndTime, Digest, Enumerable, I18n, Kernel, Mail, Mime, Minitest, Rails, SecureRandom, Singleton, TestUnit

Classes:

Array, Benchmark, BigDecimal, Class, Date, DateTime, Delegator, ERB, FalseClass, File, Float, Hash, IO, Integer, Method, Module, NilClass, Numeric, Object, Pathname, Range, Regexp, String, Symbol, Time, TrueClass, UnboundMethod

Exceptions:

Exception, LoadError, NameError

Instance Chain:

self, Java