RD on the desktop, legally anyway, isn't going to allow you to use a desktop machine without locking the display. That's what remote assistance is for. It can be configured in group policy to the hilt, so while there are some front-end configurations you might have to do in policy, once that's done it can be as easy (or easier, in fact) than remote desktop. Otherwise, you're limited to using things like VNC, which you already stated you wanted to avoid.