Play it on https://tetris.felixguo.me/!
If you've ever played Facebook's Tetris Friends game, it works exactly like this.
I found it really tedious to match up with a friend to challenge them. The Tetris Friends game also has a lot of ads, especially when playing on Facebook, making it annoying to get a quick game going. It was also hard to setup group playing.
This version is really quick to setup, mechanically works the same, and has no ads.
This repository can be super easily hosted on any server that supports Node and Express simply by cloning this repository or by using the Dockerfile included.