There's probably plenty more out there, but Hemingway, Grammarly, and ProWritingAid are pretty great.
I'd say PWA is the most robust because it has so many options and filters, but that 500 word cap on the free version is a killer, especially if you have whole chapters you want to comb through (and you're not super patient and/or have a subscription lol). Grammarly is a great intermediary because it lacks that cap and is comparable in terms of power. Hemingway leans more on the "stylistic editing" side imo, like "shorten this sentence, change this up to make your intent clear, etc." which is useful in its own way!
hope this helps?
