You'd think Tetris with triminoes instead of tetrominoes would be easy, but these are hinged triminoes. http://www.javascripter.net/games/threes/index.htm
I didn't find it all that hard. The general feel of the shapes of the pieces is similar to Tetris, minus S/Z. It's definitely much more playable than pentominoes. Solvable how?
True, the L and J missing their corners feel like the L and J tetrominoes or the S and Z tetrominoes. But the game as a whole feels much different, primarily because of the \ piece. Most sub-1G versions of Tetris encourage a nearly flat playfield, but this game actually encourages a stairstep shaped playfield. Perhaps you're used to stairsteps from 20G pyramiding in TGM series. I guess "solvable" might refer to something like my solution of Tetris under the Random Generator.
I'm guessing it was designed with the numpad in mind, but the buttons don't work. I don't think I really like the flip idea either...