The most common ones are the Unity and Unreal Engine 4 game engines. If you exclude those you'll get into my-own-engine territory pretty quick.
With the two aforementioned engines it is just a matter of connecting the HMD to your computer, making sure it works, starting up an example scene in the engine and clicking "view in VR".
For a lot of things you can just use the 3D scene as projected on your monitor, you don't need to wear the HMD all the time.
On VR gatherings I see even more GearVR's than desktop PCs with HMDs since the GearVR is just so easy to carry around and demo something to people. The disadvantage is that it doesn't have positional tracking (which adds a lot to the immersion for most applications).
I'm not familiar with the GearVR workflow though. I guess mostly the same as the PC workflow except pushing the application to your phone has a longer iteration time.
https://developer.microsoft.com/en-us/windows/holographic/us...
Also, there are some cheap headsets for your phone.
http://www.pocket-lint.com/news/132945-best-vr-headsets-to-b...