The European Central Bank (ECB) has recently published a report covering the Digital Euro experiment that was launched in September 2020 by the Eurosystem’s High-Level Task Force on Central Bank Digital Currency.
This experiment used a tiered model, and it was the Tier 2 the one which was made of multiple coexisting and interoperable systems, exploring three different types.
A fork of both Tezos and NEM where used in order to enable the implementation of a value-based Tier 2 system, as specified.
The Tezos fork was private, and the NEM fork was customized. It may indicate that in they have used these forks as testnets.
Additionally, other two distributed ledgers were used to enable the implementation of both an account-based and value-based Tier 2 system. In this case, Hyperledger Besu and Hyperledger Fabric were the chosen ones.
The report concluded that the results of the experiment do not pre-empt any decision or commit the Eurosystem to providing a digital euro. The main goal was to provide input on design questions, thereby supporting policy discussions and design decisions on a possible digital euro.