Text presentation streamed from the Internet, often via the Web using the RealPlayer plug-in; may be a text-only stream, or may be combined with an audio or video media stream.
Program(s) that open rt files
Mac / Windows: RealNetworks RealPlayer or Web browser with Real Player plug-in installed
Information from FileInfo.com - The File Extensions Resource.
http://www.fileinfo.com/extension/rt
