Tetrinet

TetriNET is a multiplayer online Tetris game for up to six people, developed by St0rmCat in 1997 that supports team play. The last official version is 1.13. The game was originally developed for Windows and was later ported to other systems.
St0rmCat released TetriNET 2 in 2000, which features improved graphics, more types of special blocks, additional features (such as hold piece and block shadows), and a master server.