Nebula is an open-source overlay network that connects servers, cloud instances, laptops and mobile devices through encrypted connections, regardless of their physical network location. Engineers at Slack released it as open source in late 2019 under the MIT licence. Organisations use it for site-to-site links and remote access, as an alternative to IPsec tunnels and traditional VPN setups. The software is distributed as downloadable code and runs on the organisation's own infrastructure.
The hosted Managed Nebula service is offered by Defined Networking, Inc., which builds on the project. Its data processing addendum gives a contracting address in Santa Monica, California, so the company is a US provider subject to US jurisdiction, including the CLOUD Act. The addendum includes EU standard contractual clauses for transfers from the EEA, Switzerland and the United Kingdom, but does not say where managed-service data is stored. A European organisation that runs the open-source code itself keeps the network under its own administration; the managed service adds a processor relationship with a US provider.