Try grepping your lib directory sometime. In fact, let me do it for you, on a relatively clean install:

time, benchmark, irb, pry, rubygems, resolv, erb, rake, open-uri, debug, rack, cgi/util, optparse, getoptlong, bundler, activesupport, actionpack, activemodel, erubis, slim, haml, sass, sequel, roda, nokogiri, rugged, faraday, mime-types, thor, test-unit, tzinfo, mail, ffi