Software that use the MIT License include Expat , PuTTY , Mono development platform class libraries , Ruby on Rails , Cakephp , Twisted , Lua 5.0 onwards and the X Window System , which the license was written for . Software packages that use one of the versions of the MIT License include Expat , PuTTY , the Mono development platform class libraries , Ruby on Rails , Lua ( from version 5.0 onwards ) , and the X Window System , for which the license was written .