latex2rtf is a translator program to convert LaTeX formatted text files into “rich text format” (RTF) files. RTF is a published standard format by Microsoft. This standard can be ambiguous in places, but RTF is supported by many text editors.
latex2html is a convertor written in Perl that converts LATEX documents to HTML. This way e.g. scientific papers - primarily typeset for printing - can be put on the Web for online viewing.
In brief, latexml is a program, written in Perl, that attempts to faithfully mimic TeX’s behaviour, but produces XML instead of dvi. The document model of the target XML makes explicit the model implied by LaTeX.