The NoMachine NX Client is closed-source software, developed under a proprietary license (EULA). NoMachine makes the software available in binary form under a free for commercial and non-commercial use license similar to the Adobe Acrobat reader software that you find in all the Linux distributions (ie. users do not have to pay to install the client software, plus you can download it and install it as many times as you want. P

Creating a OSS version of the client is easy. NoMachine develops and releases under the GPL license all the tools required to create such an open source version. NoMachine also helps the free software developers in ensuring that their OSS version works seamlessly with the commercial NoMachine software.http://www.nomachine.com/sources/

The amount of code to be written to implement a compatible client is fairly small. The NoMachine OSS components do 90% of the work that is supposed to be done by a fully functional NX session. The NX Client is required to set up and control the daemons on the user's workstation (like the X display), to manage the connection to the NX Server, to negotiate the session and to provide a minimal GUI to be used by the local proxy code to interact with the user.