I use RDP to access a Terminal server the DOES support true multi monitor, on Ubuntu using freeRDP I can use multiple monitors, but when trying to "minimize" freeRDP to use the local machine freeRDP bogs down and inevitably crashes. My question is, is there a better way to launch freeRDP other than "xfreerdp /multimon /f ..." or is there a GUI front end that will better handle hot swapping from the remote windows to the local machine.
Remmina is probably the most popular RDP client on Linux. Not sure if it is exactly what you are looking for though.
I use remmina myself on a local 1Gbit lan and it worked well for me.
As best as I can tell Remmina does not support the multi monitor launch option natively, although there may be a way that I don't know about to force it to use multi monitor.