I had a bit of trouble finding documentation for how to make a re-sizable window for Hololens and thus want to document my findings here. As this is all fairly new please share your findings in the comments.
Here is the goal... in 2D form:
On the device you can click and drag (manipulate) any of the blue cubes to scale the window. And you can click and drag the center circle to re-position the window in 3D space.
If you have a device you can find an example of this by opening the Photo app and clicking resize in the top right corner.
First and foremost make sure you are up-to-date with the latest Unity build which currently is 5.4b16: http://unity3d.com/pages/windows/hololens
Otherwise you may crash while trying to listen to the manipulate gesture.
If you aren't familiar with Gestures you can learn more about them in detail here: https://developer.microsoft.com/en-us/windows/holographic/gestures
Manipulate is going to be our focus since we are going to move/re-size based on the user's hand movements.
Microsoft's Holograms 211 tutorial will get you most of the way there. Namely the GestureManager code though their example uses both Navigation and Manipulation which adds a bit of complexity as you can't use both at the same time. Since we only need Manipulate we can nix the Transition code and just add the GesturesSettings.ManipulationTranslate to our recognizer we are using for tap. I'll share my code below.
Integrating with HoloToolkit:
Microsoft's HoloToolkit code base's GestureManager is different than the one in the tutorial. I decided to try to pick and choose bits from the 211 tutorial and drop it into the Toolkit code but ended up with a half baked solution. You could manipulate items while gazing at them but as soon as the item lost your gaze the manipulation would stop. The trick is to make sure you Override the focusedObject. Otherwise when the focus object changes the gesture is cancelled.
This class mixes the HoloToolkit code with the Holograms 211 Tutorial and makes adjustments to handle the change in focusedObject.
To handle these events you will need to wire something to catch the starts and then update while manipulating. I have my corner buttons catching the start manipulate calls and then triggering StartScaleManipulation while my center button triggers StartManipulation. Code below:
Custom Hand Manager:
I am not sure if we added the FocusedGameObject or if that was originally in the HoloToolkit and since removed. In either case, this is the HandManager we are using. Feel free to rename to HandsManager or customize how you see fit.