For hosting common files it's ok. Also it is on Android too do, great to transfer files between your Windows and your phone. But if you want better security you have to subscribe a monthly offer.
Dropbox - Online Sync and File Sharing
BookWidgets - BookWidgets is an excellent application that let you create engaging exercises in minutes and easily share a varied variety of beautiful and fun activities with your classroom and others.
Google Drive - Access and sync your files anywhere
Padlet - Visual boards for organizing anything.
Mega - Secure File Storage and collaboration
Socrative - Socrative helps teachers engage the class with educational activities to measure and visualize...