Fedimint is a modular federated e-cash prototype still under heavy development written in Rust. It already supports all main operations (deposit/withdraw via both on-chain Bitcoin and Lightning, e-cash transfers) and comes with a rudimentary CLI client. Some features are still missing and blocking mainnet deployments, but the project is moving quickly. If you are interested in contributing check out the GitHub repository.
This section contains the original architecture details shared on the Fedimint implementation.