CompuServe was the first major online service provider in the U.S. with its origins going all the way back to 1969. It reached its peak in the early 1990s when it was surpassed by AOL. Of course, both were surpassed by the rise of the Internet and more generic Internet Service Providers soon after. CompuServe peaked around 1995 with about 3 million users.
Like all such services of the 1980s and 1990s, CompuServe was a proprietary service. Internet service started to a limited degree in 1989 with e-mail being gated to and from the Internet. Web access became available in 1995. By 1997 CompuServe started converting its forums to HTML and in 2004 the proprietary interface was finally discontinued completely. CompuServe’s forums did not cease altogether until the end of last year (2017) after 36 years. Some of the active ones have found homes elsewhere on the Internet.
The above ad is from 1994. $8.95 got you unlimited connect time and included various features including 60 e-mail messages a month. Some services cost extra.