BitTorrent Sync by BitTorrent
BitTorrent Sync by BitTorrent, Inc is a proprietary peer-to-peer file synchronization (File synchronization is a process of ensuring that files in two or more locations are updated via certain rules.) tool available for Windows, Mac, Linux, Android, iOS, Windows Phone and BSD. It can sync files between devices on a local network, or between remote devices over the Internet via allegedly secure, distributed P2P technology.

BitTorrent Sync synchronizes files using Peer-to-peer (P2P) technology.[11] User's data is stored on their local device instead of in a 'cloud', therefore requiring at least one device, or "Node" to be online in order to synchronize files. BitTorrent Sync encrypts data with an Advanced Encryption Standard AES-128 key in counter mode which may either be randomly generated or set by the user. This key is derived from a 'secret' which can be shared to other users to share data. Data is sent between devices directly unless the target device is unreachable (e.g. behind a firewall) in which case the data will first be relayed via an intermediary node. Many devices can be connected simultaneously and files shared between them in a Mesh networking way.

There is no limit on the amount of data that can be synced, other than the available free space on each device.

BitTorrent Sync by BitTorrent is not a cloud alternative but, definitely looks promising & still it is in beta.