azw3 The American company Amazon is a recognized powerhouse when it comes to all things related to books. Their proprietary eBook readers dubbed the Kindle which was first released in 2007 is a testament to this. The .azw file format is the filename extension associated with eBooks designed to be read on Amazon's proprietary Kindle device and through their free but closed source Kindle software for smartphones, PCs, and Macs. The format is incompatible with any device other than kindle and its associated software. In order to open files saved in this format on non-kindle devices, one would have to convert the file to another format such as the open ePub format or PDF. Some converters can also convert other formats into .azw files which can later be opened on a kindle device or application.
rb The .rb extension is used for many formats which include definition files based on the Fuzzy rule, eBook files of the Rocket Edition, class files of Ruby on Rails, project files of REALbasic and the profile configuration files of Rosebud. Other versions of Ruby which are also called gems include Mongrel, Capistrano and Ruby on Rails.