It can monitor smart contracts activity and interactions based on generated transactions and events.For example, It can be used a local blockchain explorer that runs locally on your server or machine ,or as an investigation tool that scrapes the blockchain in search for a specific query. This is done by sending requests to an Ethereum node via JSON RPC calls. There are public Ethereum nodes that can probably be used for this.

A protocol for timestamping arbitrary stuff and storing it in the Bitcoin blockchain for posterity. Can be used for arbitrary data, by default documents dragged and dropped into the webpage. Easy to verify, too. Public submission servers exist. Proof of concept implementations in Python, Javascript, and Ruby. Seems kinda gimmicky, to be honest, but a use might emerge later.

blockchain.info has a realtime ticker of Bitcoin transactions that their processing nodes have received through the blockchain but haven't yet been recorded as being confirmed as valid.

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