User experience that is close to word. No source code. Compatible with the needs of non-tech-savvy users.
Definition (Wikipedia (en)):
The Rich Text Format (often abbreviated RTF) is a proprietary document file format with published specification developed by Microsoft Corporation from 1987 until 2008 for cross-platform document interchange with Microsoft products.
Most word processors are able to read and write some versions of RTF. There are several different revisions of RTF specification and portability of files will depend on what version of RTF is being used. RTF specifications were changed and published with major Microsoft Word and Office versions.