I see some kind of ambiguity in answers here :-)
I'd suggest to tell technologies and underlying protocols apart.
VNC: uses RFB protocol.
Apple Screen Sharing [SS] (which is enabled by checking "Screen Sharing" in System Prefs): it is a vanilla VNC plus some Apple-specific extensions, e.g. pasteboard auto synchronization, display selection, screen locking, encryption, drag & drop and file transfer in latest servers. Another thing it has is the Apple-specific "codec", which is easy to recognize by JPEG-like artifacts. It also includes new authentication types (by username and password and by requesting permission from remote user) and the very feature you're discussing - Session Select, which allows you to log in as active user or to create invisible ("virtual") user session.
Apple Remote Desktop [ARD] ("Remote Management" in System Prefs): uses Apple Screen Sharing as a base for the screen sharing and another very different protocol (name it ARD protocol for instance) for computer management things, like performing spotlight searches, running shell commands, sending messages, transferring files and so on.
@zneak asked for a client that supports Session Select feature. Unfortunately, as far as I can see, even Mac OS X clients rarely support Apple Screen Sharing features. These are: first, Apple’s built-in Screen Sharing client; next goes Remotix for Mac, which seems to support almost all of SS features including Session Select; JollysFastVNC which supports Apple authentication, display selection and screen locking, and Screens for Mac that supports only Apple authentication.
As for Windows, all I could find was already mentioned here Remotix for Windows, though it was marked as beta for a long time.
Probably all these things are obvious for some of you, but I spent a good couple of hours sorting it out. Hope this post will save some time to someone :-)