We're big fans of Echo here at Datum, and sponsor the project where we're able. The main version of Echo is v4, but there's been lengthy discussions about a v5 which have not yet manifested. After thoroughly reviewing the v5 changes and comparing them to the v4 branch, it would be a very large undertaking to adopt in the future if we took the v4, so we've elected to create + manage an ongoing fork of the v5 branch and pull in bug fixes, features, etc., from the main codebase.
The Echo creators / maintainers licensed their software as MIT, any additions to their original works falls under the Apache 2.0 license in this repository.