The free NSO download is for evaluation purposes only, and cannot be used for any production use. It comes without any support, although you can of course ask questions here on the NSO Developer Hub.
The NSO package comes with a lot of examples (in the examples.ncs directory in the installation), and these have NEDs that are sufficient to run these examples. You may also connect to real (physical or virtual) devices in your lab. They are however limited, and have nowhere near the coverage of the production NEDs. For access to production NEDs you need to purchase lab licenses for NSO and the required NEDs.
The current free NSO eval package is 4.7.0. This is the complete NSO server package. We will periodically, but infrequently, replace the server version. However, if you require any other version then you need to purchase a lab license, which provides access to all currently supported versions.