iNetris is a multiplayer internet tetris clone which allows for 2 or more players.
The latest version (and final?) is 2.0. and was written by Samuel Marshall.
This program is shareware, and costs $10 u.s. to register.
It is like multris in the fact that it is just pure tetris and allows the background
and other minor things to be changed.

Here is a screenshot of it in action: