Concurrent Remote Graphic Session

I know that a lot of people already asked this for older OS. But I was wondering if it is possible to have a windows computer connect to a mac without interruption to the user that is logged in an account on the mac. I just want my windows computers to access the mac remotely without logging the current user out. I don't want to telnet or ssh I want to remote control it. I am wondering if it will be a graphical user interface.

Thanks in Advance

iMac 27", core i7, 8gb of ram, 1tb HD