azw4 .azw4 file extension is a file format developed by Amazon and is used by applications specifically designed for e-readers. It is mainly found on Kindle e-reader devices, a Kindle software is also available for desktops that allows interpretation and reading of azw4 files. It is used to read e-books normally purchased online. The greatest benefit that comes with using azw4 is that text does not have to stay static, so files transferred from a device with a larger screen to one with a smaller screen are adjusted and one does not have to zoom in order to read.
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.