OpenNX is described as 'open source drop in replacement for NoMachine's NX client. It is compatible to the original client in that it uses the same syntax for the session configuration files (.nxs files)' and is an app in the Network & Admin category. There are six alternatives to OpenNX for a variety of platforms, including Mac, Windows, Linux, Online / Web-based and Android. The best alternative is AnyDesk. It's not free, so if you're looking for a free alternative, you could try NoMachine or Net Meeting. Other great apps like OpenNX are LogMeIn (Paid), screensy (Free, Open Source) and RemoteCall (Paid).
LogMeIn gives you fast, easy remote access to your PC or Mac from your browser, desktop and mobile devices. Premium features like file transfer, file sharing and remote printing help you stay connected and productive wherever you go.
Net Meeting provides a free solution for web conferencing, audio and video conferencing. Share your full screen with colleagues from around the globe. It enables you to invite attendees from inside and outside and monitor all meeting activities.
RemoteCall is a cloud based remote support solution bridging the agents and clients. Support client PCs, multiple displays, Windows, Mac and Linux as SaaS service or in-house server solution. Best solution for IT professionals.