The Axon Framework and its documentation itself is open source and licensed under the Apache License v2.0.
AxonIQ Axon Server is a commercial software product by AxonIQ B.V. Please contact AxonIQ via https://axoniq.io or sales@axoniq.io if you are interested in acquiring a license and support contract. To facilitate evaluation and development, AxonIQ offers a free edition of the software.
The Java client to Axon Server is open source under the Apache License 2.0. It is available through GitHub (https://github.com/AxonIQ) and can be downloaded from Maven Central.