En réponse à Pierre.

I don't see what could prevent it from working offline (well, if you use the client app, it will still have to be able to exchange with the server).
The client part and the server part are free.

On the other hand, the documentation for setting it up is brief (not least because running software like whisper is not always easy). https://framagit.org/framasoft/lokas/

So, for the time being, the answer is ‘yes, but you need good technical knowledge’.
If we have the financial resources, we can free up some time to improve the documentation and document different installation scenarios.