Windows Mixed Reality does this, and remarkably well. Launch an app from the VR "start menu" and it'll open as a floating window positionable in 3D space. Bonus is that you can use your mouse and keyboard still in VR, with mouse / keyboard focus on the window you're gazing at.

Downside: as far as I know, you need a WMR headset to use it. There might be mods to use the Mixed Reality Portal (the VR window manager) with other headsets, though.

Here's a random YouTube video demonstrating it: https://youtu.be/gPkcDg8IECU