It would be very nice if there was a desktop client as well. Now you say why on earth one would want that? Well if you have 2 pcs with one graphics tablet (one Win one Lin for instance), it can help to swicth between desktops without much pain.
Another use case would be to use a windows tablet as a client like we use the android ones.
There's SOGOConnector for Thunderbird, for example. That works quite nicely for me.