After trying out a few different options I think https://promova.com/page/speaking-app provides a good balance of theory and practice. It is suitable for various levels and the fact that it has a strong focus on culture makes it more interesting than a standard textbook. While no app can do the work for you having a reliable tool like this definitely makes the path to fluency a lot smoother. It is a solid investment of time for anyone serious about improving their speaking skills in a modern and efficient way.