The 3d rudder aims to give PSVR games the option of full locomotion when using the PlayStation Move controllers.
The PlayStation Move controllers lack an analogue stick for movement, there are some control schemes that do their best to bypass this shortcoming, the Skyrim scheme seems to be the best option for now.
The Move Controllers give you hands in game, the 3d rudder gives you feet. Whilst sitting simply place your feet on the controller and tilt in the direction you want to go, the degree of tilt affects your movement speed.
Good news, lots of games are already compatible and there's more to come.
I haven't had the chance to get my hands (feet?) on the 3d rudder but from what I've heard from people who have is good.
For more info check out their website or follow 3d rudder on twitter.