TightVNC is a free remote control software package. With TightVNC, you can see the desktop of a remote machine and control it with your local mouse and keyboard, just like you would do it sitting in the front of that computer. TightVNC is:
- free for both personal and commercial usage, with full source code available,
useful in administration, tech support, education, and for many other purposes,
- cross-platform, available for Windows and Unix, with Java client included,
- compatible with standard VNC software, conforming to RFB protocol specifications
It is great, simple, free and well documented/supported. I have been using it for decades and highly recommend it.
But, of course, your clients have to install it too (they as server, you as client)