Rio is a window manager for X which attempts to emulate the window management policies of Plan 9's rio window manager. Rio is derived from David Hogan's 9wm.
It pretty much sucks, on UNIX.
This is not a slam on David's work. It's an observation of how poorly the concepts translate to the UNIX environment — all of the text based control mechanisms from the real rio on Plan 9 are completely absent.
That said, the 9term terminal window program (also from plan9port) goes some way towards replicating the on-screen experience of manipulating text in rio windows. It remains a little buggy (random crashes, doesn't always open up at the correct size inside tiling window managers), but is, ultimately, preferrable to a TTY.
Rio is included with plan9port, which is available in the OpenBSD ports tree.