If you are familiar with the POMT app, this app may interest you. While the original POMT app covered cells and genetics, this version focusses on bones.
You can zoom in to the bone at different levels of intensities to see all of the components that make up our skeletal system.
The design is simple, but there is plenty of detail in the content. You can even view a broken bone and the stages of it's healing. Once you get to a few levels of magnification, you do reach the same items as in the Cells and genetics version, although this shouldn't put you off as this version is currently Free in the app store.