Ubuntu – How to set up remote desktop

The simplest thing to do (requires almost no set-up) is just using SSH to tunnel X connections. SSH can forward your local computer's x-server connection to the remote computer. That way you can run a program on a remote computer but display it's windows locally. The performance isn't too great though. If your contractors are using Windows then they'll need to download Putty and Xming. You can also tunnel VNC over SSH if they have a VNC client, but VNC's performance is even worse.

If you want to minimize the time you are paying your contractors to look a loading screens then you'll probably want to use NX. While X works remotely it's not optimized for non LAN networks. NX fixes this by using compression and getting rid of redundant Xlib calls.

While the NX client is free, NoMachine's NX-server isn't. Luckily, if you don't mind a little work, you can use Google's NX-server NeatX. NX uses SSH tunneling behind the scenes so it is as secure as ssh -X. And doesn't require setting up a VPN.

If your desktop machines are behind a NAT or a proxy though, you'll need to use a VPN.

Setting-up a VPN is a little bit of work though. Luckily I find the community documentation of OpenVPN to be pretty easy to follow.