Common Gateway Interface (CGI) programs live on a server and generate HTML pages "on the fly" in response to requests from users.
These programs convert files from one format to another. For example, the popular rtf2html filter converts Rich Text Format (RTF) files into HTML. RTF is commonly used to move formatted text from one type of word processor to another. The rtf2html filter takes these intermediate files and converts them to HTML.
ftp://uiarchive.cso.uiuc.edu/pub/systems/mac/info-mac/text/html/rtf-to-html-301-ppc.hqx
http://www.med.ufl.edu/medinfo/mtx/