Another I've enjoyed is Squibler. Unfortunately its replies are limited to 4000 words per month (or is it just 4000 characters), which you can burn through in five minutes, unless you pay. Then you get unlimited usage for the duration. I haven't used it to complete a story-- it would probably elicit something either bland and obvious or completely off-topic. But I wrote one paragraph by paragraph, highlighted a section, and clicked on either "Describe" or "Expand". The responses appearing in the right column, next to my own text, can be substantial and are usually fun to read and save. Only rarely do they get the facts wrong or contain anything ridiculous. It's remarkable how they sometimes almost read my mind, correctly divining a character's motives, even though I may have only implied them. For instance, "He bought the car with the intention of getting stuck in it." In addition to your basic text, you can create characters and list their personality traits or other attributes. Presumably the program takes all these into account when a text you highlight specifies who is doing what.
We are warned in general that these systems recognize and reject attempts to produce pornography, so I didn't want to cross the line. But what I wrote was sometimes extremely sensuous and suggestive. A human reader would see that it was erotica immediately. But the program played right along. Sometimes a response was even more so. Not being too explicit probably makes for better writing in any event. After all, not even we always know what would turn someone else on. It will be awhile before AI knows that better than we do.
"Expand" usually produces two responses, "Describe" perhaps three or four. Once they appear, be careful where you click. At the bottom of each response is an icon for copying it to the Windows clipboard, from which you can paste it into Notepad. Then click somewhere on
the response column to scroll. If you click elsewhere, the responses instantly disappear.
Reviewers suggest alternative systems that they like even better than Squibler. I'm eager to try some of them.
