The engine is named Garlic, which is the same engine as TOJ's client. (Try searching "GarlicImpl" in tetris.exe)
List of interesting things from Tetris Dash (dash_090707_toj_594px.swf):
- O Tetromino doesn't rotate at all.
- There is an unused class named "TetrisAI". Probably they wanted to put AI battle?
- There are some partial implementations of Anti Miss Drop item.
- There are some partial implementations of Replayer.
- There is a protection that prevents the game from working on local drive. But the protection is simple. It just checks the existence of "http" in the URL.