What is "blocktrix"

Blocktrix is a free, online, multiplayer, puzzle game based on TetriNET and was created in 2000 by StrikeLight. It was developed as an update to the official TetriNET 1.13 client after the original creator, St0rmCat, created a new version to the game entitled TetriNET 2, which included major changes to the TetriNET client such as not allowing private servers. While Blocktrix is compatible with TetriNET servers, the Blocktrix protocol itself adds features to Blocktrix specific servers which makes it a different game altogether.