rtftohtml is available for UNIX, Macintosh and PC systems. Binaries can be copied directly from Chris' ftp directory at Cray, but note that these binaries were not extended by rtftoweb.
rtftoweb is currently only available for UNIX, but you are more then welcome to try and port it to Macs or PCs. This should not be too hard, since rtftoweb does not use any UNIX-specific features, maybe apart from filenames longer then ridiculous 11 characters (concerning a port to PCs).
For directions on getting and installing rtftohtml and rtftoweb on UNIX systems, read the next section: Installing rtftohtml and rtftoweb.