Reading Teacher is a site that’s been around for awhile. There used to be a cost involved, but just last week they made it free-of-charge.
It has one or two hundred online books for very beginning readers — sort of an expanded version of Starfall. Many of the books have short quizzes after them.
It’s free to individual users, and it’s free to create a virtual classroom of 30 students to track their progress. The site says that if you have more students, you can just create another free account using a different email address to create a second virtual classroom.
I am using it, and will in the future, as another option for Beginning ELLs, particularly ones who have been out of school for a long time.