Sia is a decentralized cloud storage platform similar in concept to Dropbox and other centralized storage provider where instead of renting storage space from a centralized entity, clients rent storage space from other peers. Nodes provide storage to clients using the Sia blockchain as contracts. Before storing the data, the data is encrypted into many pieces and uploaded to different hosts.
The Sia developers mined the first 100 blocks of Sia where the rewards begin with 300,000 Siacoins for the first block and each subsequent block reward decreases by 1 SC until the block reward stabilizes at 30,000 Siacoins per block.
Sia has a second cryptocurrency called Siafund where 3.9% of all successful storage contract payouts go to the holders. The Siafund is 100% premined with 10,000 units in total, of which 87.5% is owned by Sia's parent company, Nebulous Inc. Siafund is created to finance the early development of Sia without relying on donations or premine.