libecat-sdev is a free implemention of an EtherCAT SubDevice stack.
To create and/or sell EtherCAT SubDevice product you have to be member of the EtherCAT Technology Group (https://www.ethercat.org) and retreave a vendor-id from there. The EtherCAT Technology, the trade name and logo "EtherCAT" are the intellectual property of, and protected by Beckhoff Automation GmbH.