Bitrix24 is a free cloud server that comes with over 30 handy tools, including online file storage and sharing, document management,
real time communications (video conferencing and instant messaging server), email server, social network, CRM, project management and human resources management system. Best of all,
Bitrix24 is available as self hosted software for on premise deployment that comes with API and open source code. Migrate from cloud to your own server any time you want.
If you want to start using free online file sharing server, this Bitrix24 manual will get you up to speed quickly.
In order to test self hosted (on premise) edition of Bitrix24, you need to download it from here. Please keep in mind that it takes about 1.5 hours to deploy and set it up.
Self hosted Bitrix24 manual is available here.