... are bound together by the core Common library keeping track of chain specifics and hardfork changes. They are complemented by helper packages like RLP for data encoding/decoding or Util, providing helper functionalities like (byte) conversion, signatures, types and others. Finally, the EthereumJS Execution Client (EthereumJS) has been in active development for some time now. It already serves a variety of purposes like testing, research (e.g. EIPs) and developer tooling.