As has been said, there are a number of filters that convert from native word processor input, or output, to HTML. This means that we do not have to force a "house style" on course authors at the point they write the material. We get the house style that the reader's WWW client program is configured for. It also obviates the learning of a new package by authors!
One interesting problem though with letting people author their material in many different systems is that of maintaining links. Each word processing package has its own idea of references or citations or bibliographies. Indeed, some systems even have hypertext built in nowadays, but of their own design. We would like to make sure that URLs can be associated with similar kinds of logical links in original source documents - e.g. references/citations in papers, course notes (to papers, books (ISBNs), other courses etc). Depending on the filter, it may be possible to translate these into URLs appropriately.
On the other hand, it may be necessary to persuade people to start to use different ways of specifying links in the package they are using, so that the filter for that package can translate these correctly into URLs. This latter approach is used, for example in the excellent LaTeX2html tool from Nikos Drakos at Leeds University in the UK.
Filters that are in common use include:
There are also many useful ancillary tools (pstogif) for converting pictures from one bitmap format to another.