From Hard Drop - Tetris Wiki
It has a custom rotation system that is based on SRS/ARS (selectable) that allows most of twists to be done, including T-spin triple. It also allows O-spin, I-spin tetris and diagonal slide (if left/right movement fails, it tries downleft/downright).
It uses Tetris Best rotation system.
Note: This game works best on Firefox, and turbo mode (shift+green flag). The performance also increases with a faster computer.