An re-packaging of the Rex library included in the Metasploit Framework for use by non-Metasploit applications. Originally created by Jacob Hammack and made official by the Rapid7 development team. The upstream of this package is the rex subdirectory of https://github.com/rapid7/metasploit-framework
Note that prior to version 2.0.0, the 'rex' gem was an unrelated library developed by Aaron Paterson (@tenderlove).
For users of the prior library (a lexical scanner generator), set your Gemfile to something like the following:
gem 'rex', '< 2.0.0'
This package replaces the librex gem.
$ gem install rex