> I am writing a document for our client that has accepted to work with ConTeXt. One of the things I want to mention is the different output formats. I know PDF and xhtml and that in the near future epub will be available. Are there others? (I know dvi, but I do not think it is worth mentioning.)

MkII with pdfTeX as engine supports PDF, PS and DVI as output formats but with XeTeX you have only PDF as output.

With MkIV you can produce PDF and also XML (and afterwards epub) besides the PDF.

As your client doesn’t know anything about TeX and ConTeXt i would ignore MkII and mention only the output formats of MkIV.