Siacoin is a utility token of the cloud storage platform called the Sia network. Sia is open-source and blockchain-based. The operations take place on Sia's own blockchain. The coin is used to pay for storage rent transactions. The coin is Proof-of-Work-based meaning that Siacoin can be mined. Another use for the coin is trading.
ChainLink (LINK) is the native currency of the ChainLink platform. It represents an ERC-20 token is listed on multiple exchanges paired against major cryptos. At the time of writing, you can trade LINK against the fiat USD currency on Coinbase Pro.
Smart contracts are not able to access data on their own. Since connecting these contracts to data via node is deemed as a point of failure, using a decentralized service could be a solution.
Therefore, the ChainLink project sees its mission in the integration of the off-chain data into smart contracts through a reliable decentralized oracle network. LINK tokens hit the market in 2017 and the currency quickly made its way to the top 50 cryptocurrencies by market cap. Later it reached the top 20. ChainLink partners with a large banking network SWIFT.