Whereas computer games mostly stayed around the same price point throughout the 8-bit era, application software varied much more. For instance, this word processor, The Write Stuff, for the Apple II is being advertised at $99. This was not atypical for word processing software in the early to mid 1980s and some application software cost much more. However, by the time the late 1980s rolled around, there was stuff like GEOS being given away for free with a hardware purchase and most common application software could be found significantly discounted.
As far as 'The Write Stuff' goes, I don't know that much about it. This ad comes from the May 1984 issue of Microkids and is for the Apple II version but I know there was also a 'The Write Stuff 64' for the Commodore 64 and possibly other versions. It seems relatively hard to find much information about this particular software so I would venture to say it was not the most popular word processor. Having said that, there were tons of word processors available in 1984. These days word processing is mostly dominated by Microsoft Word, Google Docs, or a variation of OpenOffice or LibreOffice but in 1984 there were dozens of viable choices.
These days there isn't much reason to use 8-bit word processing software. Some people like the look and feel and minimalism of some of the older apps. However, I would want at least 80-columns and something that is responsive with large-ish documents. Something the Commodore 64 and Apple II did not offer by default.
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