The D3A is a decentralised energy exchange developed by Grid Singularity to enable a decarbonized, decentralised, democratised and digitised energy system. D3A stands for Decentralised Autonomous Area Agent. In its core, the D3A exchange is the set of smart-contracts necessary to create decentralised energy exchanges with a low barrier of entry. Hence, D3A allows energy devices of arbitrary scale to trade with their peers on a scalable market platform. The D3A exchange engine is available open-source under the GNU GPL license (https://github.com/gridsingularity/d3a). The D3A UI allows users to interface with the D3A exchange engine through a user-friendly web app, available as a beta version for developers at d3a.io. Energy companies and consumer groups can use the D3A UI to improve operations and make investment decisions, leading to potential deployment of the D3A exchange engine to efficiently run their decentralised and distributed smart grid. In brief, the D3A showcases and harnesses the potential of transactive grids, renewable energy sources (RES) and peer to peer (P2P) energy trading for all stakeholders in the energy transition. You may watch the D3A presentation here. To initiate collaborative projects please contact us at firstname.lastname@example.org.