Rio is the terminal multiplexer in Plan 9
Besides that name clash, it apparently competes with another terminal emulator that was creatively named "vt100".
Scrolling over the page I did a double take when I saw the benchmark. No way a vt100 can do 221 MiB/s! Who even types that fast anyway?
It's nice to see it running in novel places like the Steam Deck, Windows, and FreeBSD.
Are there any examples of the browser support advertised on the front page?