You can usually do it with shared Google docs. I know a few writers who share their content with a few trusted betas. It provides the necessary features, I thin

You can usually do it with shared Google docs. I know a few writers who share their content with a few trusted betas. It provides the necessary features, I think. Highlights, commenting etc. I think there is also a "real-time" feature that it provides (not sure about that), so there is usually more than one eye on the doc as the chapter is being typed.