Nav CIS
NavCIS, originally known as CompuServe Navigator, is a client program which was used to automate connections to the CompuServe Information Service at a time when online use was priced by the minute. It was available for MS-DOS and Microsoft Windows as a GUI on both.
NavCIS was one of the first e-mail and forum clients to feature WYSIWYG e-mail in the early 1990s.
For a while, a Macintosh version called 'CompuServe Navigator' was also available, which fulfilled the same function. It ran on MacOS 4.1 up to 7.1, and made it to at least version 3.2.
Read more about Nav CIS: Other Clients