Por si algún profe quiere investigar sobre estas 70 apps y ver si le son de utlidad. Yo uso algunas // The 70 Best Apps For Teachers And Students - Edudemic. These are listed as itunes apps, but I'm sure a lot of them can be found for Android as well.
The internets biggest and most complete list of free software for all students. Whether you are in the arts humanities, liberal arts sciences, engineering, architecture or any other major you should find it useful for your studies and for your budget too.