It's a REST API in a server that accesses Ethereum. It's not a smart contract running directly on Ethereum. Rather it accesses smart contracts which themselves are 'on' Ethereum.
39 karma · joined February 24, 2014
In the case of ETHEREST - it's just about being able to grab a contract address and call any method on it quickly and easily. Having to hook into a a node & provide an ABI gets frustrating really quickly, especially when you're testing.
On stability - it's definitely an MVP right now. Our plan is to open source the innards soon to a) make submitting transactions trustless and b) share some of the innovations we've made to make this scale well.