Sia is a network of decentralized storage created by Nebulous Labs. Using a peer-to-peer decentralized network, it creates a marketplace of cloud storage where some users act as hosts that offer free space in their disks and other users act as renters that pay for using that storage space.
According to its creators, the ultimate goal of Sia is becoming the backbone storage layer of the Internet. Anyone can rent his unused hard disk space, thus creating a network of decentralized datacenters.
Sia software is licensed under the MIT license and its code is open source, meaning that independent developers can contribute to the software and build new applications on top of it.
Sia uses its own blockchain to store all token transactions, file contracts, the database of hosts and the proofs of storage hosts have to fulfill to demonstrate they are actually hosting the files. The blockchain also enforces the payments associated to the file contracts.
The blockchain is secured by the Proof of Work algorithm Blake2b, being miners rewarded with newly issued Siacoins. The reward will decrease over time until it reaches 30000 Siacoin per block. This means the inflation is reducing over time in a predictable fashion.