The Rich Text Format (often abbreviated to RTF) is a proprietary document file format developed and owned by Microsoft since 1987 for cross-platform document interchange. Most word processors are able to read and write RTF documents. Unlike most of the word processing formats, RTF is human-readable. RTF is also the basis for Windows Help (Winhelp) format.
See also Ratfink, a Tcl library for generating RTF files.
O'Reilly has an RTF pocket guide , the only book I (EKB) know of that documents the RTF format.