This is a very small task-switching app.
When you invoke LastApp, it switches to the last opened running app, as pressing Alt+Tab on a PC. It is useful to assign LastApp to a swipe or a key combination by a some sort of quick-launcher.
By "LastApp Setting", you can exclude an app from LastApp. Choose apps that not to be switched by LastApp, and clear the checkboxes. In general, exclude launcher and home apps.