AMULET3i is the third generation asynchronous ARM-compatible microprocessor subsystem developed at the University of Manchester. It is internally modular being based around the MARBLE asynchronous on-chip bus, and is also extensible through the addition of conventional clocked synthesizable peripherals via an on-chip synchronous peripheral bus. As such it is capable of forming the core of a wide range of system-on-chip applications, bringing asynchronous design into commercial use in a flexible and easy-to-use configuration. Its performance and area are comparable with clocked equivalents, and its low-power and electromagnetic emission characteristics give it unique capabilities in appropriate applications.