Oracles provide trusted datasources for the public blockchain. A good introduction on the subject is available here.
Oraclize is using the TLSNotary proof (stored on the IPFS public network) to prove that the data provided to the smart contract comes from a trusted source and has not been altered.
A single Oracle, even if the provided data is cryptographically proven to be unaltered and coming from its trusted source, can always alter data for his own benefits. Gnosis goes one step further and creates a market for Oracles, adding crowd wisdom (or “coopetition”) to validate provided data by a consensus among competing oracles. Oracles stake some tokens to remain honest and are puished for behaving badly. With the distributed oracles, you can trust the data quality.
Gnosis extends the notion of current data to future data by providing prediction markets. Historically, Augur is also working on providing decentralized Oracles, with the differences between the two approches being analyzed here.
Rockchain.org is bringing a new way to seamlessly provide static (and in the future dynamic) information to Oracles platforms such as Oraclize, Augur and Gnosis. We’re not competitors, but provide a way to easilly share some data just by having a shared folder locally, while our DappBox client will prove your identity and keep track of any proof of data content and transfers. Any Rockchain DappBox (called technically FactMap nodes in our WhitePaper) node can become an Oracle and share data. Which data should be published in Oracle platforms will be defined in our datascripts (our decentralized scripting engine, also described in our WhitePaper).
Rockchain distributed file system is based on a simple concept: every nodes keeps its data local, and defines how other nodes can access those data with blockchain-based access rights. Similarly to UNIX file system access rights, there is Read access, Write access (collaboration on files). In Rockchain, eXecute rights (X) means that the node has an ability to opt-in for which public datascript will be executed locally.
In Rockchain, we also have group visibility, such as UNIX file system rights: local group (representing internal network), Peers (authorized nodes peers, defined in a smart contract) and Everyone.
Becoming an Oracle for some specific data simply means defining read access rights for Everyone on a DappBox node.