AlphabetTrace: I like this app because it shows a video on the side of the order in how to create the letter, but you don't have to necessarily follow the video. You also can't make the letter wrong. You have to stay in the "road" but you have to draw a line in each spot otherwise it will make you do it again. The settings are helpful on this app as well, such as the ability to adjust accuracy needed, time, etc.
Little Writer - The Tracing App for Kids: One of my students chooses this app to play almost daily during her break time! It's cute and fun, students start with the large animal or whatever it might be and follow it to eat all of the little fruits, or hay bales, or something. You have to complete each line correctly the entire way or start over. Also, I'm not sure about some of the letter formation, but it's fine for what my students use it for. You can also customize this app by adding your students name and your (or your students voice).
Those have been my favorite in the free tracing category so far. Do you have any other tracing apps that you enjoy? Please share in the comments! Thanks!