If you think about it modularity has always been at the heart of the Bitwig workflow. Devices can be nested, clips are containers, modulators exist everywhere, and practically anything can be dragged anywhere.
The Grid offers an open modular environment that gives you three different devices to start your modular sound design in; Mono Grid, Poly Grid and FX Grid.
The Grid includes:
More info at Bitwig
The philosophy of designing organismic instruments