mobi The .mobi filename extension is an eBook file format developed by French company MobiPocket for their ebook readers for mobile phones and PDAs. The company was later acquired by book reseller and online store company Amazon in 2005, a deal which included the mobi format asset. The mobi file format is mostly associated with the mobipocket software package as well as early versions of Amazon's kindle ebook reader device. The format is considered cross platform given its compatibility with several devices including most smartphones that have compatible readers installed. But although mobi files still exist in circulation, the format was superseded by Amazon's AZW format when support and further development of mobi ceased in 2011.
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.