“Version 4 of the software, in fact, will be only available under a closed source license”
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NoMachine always had an awkward relationship with FLOSS. They provided no-cost trials and FLOSS clients but kept the “server” non-free. Now the whole thing will be non-free. With X deprecated by Ubuntu, perhaps they thought they needed to cash-in while they could. We still have DXPC and openSSH along with varieties of VNC. FreeNX never seemed to flourish.