|Release||Version 6.9 released on May 6th, 2010|
|Hold piece||Yes, with IHS|
|Rotation system||Almost anything you can come up with|
NullpoMino is a cross-platform, open-source Tetris clone written in Java providing three versions: One using Slick, another using sdljava, the last using Swing. It simulates a great many games, including the TGM series, and contains a utility for creating your own custom rotation systems as well.
NullpoMino is one of the few Tetris games, official or not, with a truly cross-platform online vs. mode, the others being TetriNET, Blockbox, Tetris Friends, and MultriNet. Blockles also would have been on this list before its demise.
All of the game modes with "Mania" in their names are based directly on TGM modes, except for the two added by Zircean: Retro Mania simulates Sega Arcade Tetris, while Phantom Mania takes the Death speed curve and makes it invisible.