The original plugin was Silver Flows created by Aby Nimbalkar and Andrey Shakhmin. The private beta is currently being tested but the public beta is due for release very soon.
One of Adobe XD’s main USPs is its prototyping feature and it seems Craft have cottoned on to this. This has added pressure for XD to deliver on their list of pending features to stay in the game. A plus of all this competition is that software is developing fast and improving all the time.
If you’re a Sketch user and looking to start prototyping Craft’s latest plugin is a great place to start. Alternatively, if you’re already an Adobe user, XD currently prides themselves on their prototyping features.