The whole point of the "cloud" is to be able to scale, instantly. Tonido (and MS Windows Home Server) are just singleton, so I don't think they can be considered "cloud" solutions, simply because they cannot scale on-demand.
If Tonido was a cloud computing solution, a large amount of demand would cause it either to magically launch a new Tonido Plug, or alternatively use the resources of someone else's unused Plug server.