NULS is a blockchain with a modular based architecture enabling customizable modules and sub-chain operability. Its two-part design is the microkernel and the functional modules. The microkernel provides the underlying mechanisms for the network while the functional modules are the compartmentalized features of the blockchain. They have been built with the goal to maintain the well-known programming practice of high cohesion and low coupling. They also adopt the hotpluggable principle allowing modules to be added or removed during operation.