Ethereum is an open source platform for smart contracts built on top of block chain technology.
Novel "memory-hard" hashing algorithm specification
Use of GHOST blocktrees instead of a traditional blockchain for PoW data propagation
Use of Patricia trees in block data structures
Transactions which contain loop-enabled programmable instructions for the creation of novel derivatives and functions within the blocktree; these are deemed "contracts"
Ethereum intends to provide a blockchain with a built-in fully fledged Turing-complete programming language that can be used to create "contracts" that can be used to encode arbitrary state transition functions, allowing users to create any of the systems like:
- custom currencies and financial instruments ("colored coins")
- the ownership of an underlying physical device ("smart property")
- non-fungible assets such as domain names ("Namecoin")
- complex applications involving having digital assets being directly controlled by a piece of code implementing arbitrary rules ("smart contracts")
- blockchain-based "decentralized autonomous organizations" (DAOs).