Sia is a decentralized network storage platform that is made up of disk space donated by users from everywhere on the planet.
If you have siacoins then you can rent storage from hosts on Sia. The key to achieving this is the use of "smart" storage contracts that are recorded in the Sia blockchain. The smart contract ensures that the host is only paid once the file has been kept for a set amount of time. It helps to keep hosts careful because if they lose the file then they don’t get paid.
The Sia network is distributed, which means that latency, throughput, reliability, and security aren’t centralized and so can be optimized. Anyone on the Sia network can get paid to donate their spare storage space making cloud storage cheaper for everyone.
You can pay for storage space using the Sia cryptocurrency, and if you choose to be a provider then you will be paid in siacoins too. The storage platform isn’t in its final form yet, and uploads to the wallet are restricted to a maximum size of 500mb.