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
AlReader - Alreader.com - new perspective on reading e-books.
Google Drive - Access and sync your files anywhere
Universal Book Reader - Just like its name, Universal Book Reader is really a universal book reading application allowing you to read the eBooks from the convenience of your smartphones.
Mega - Secure File Storage and collaboration
iReader - iReader is one of the most accomplished ways to read the books right from your smartphones.