This looks like a concept based around Debian Chroot. There are several apps on the app store that will install a copy of debian in a chroot inside of android, and then when it boots, you can connect to the desktop via vnc.
Here's one app called "Complete Linux Installer" (looks outdated) that does this: https://goo.gl/5ryu5x
It certainly works, though there has definitely been limitations caused by the speed of the hardware and the latency that vnc introduces. I've never tried this on an external monitor and external input devices. There's also a gap because you need a separate vnc client.
Maru, if it exists, seems to work off the same concept, but with some polish. They have an install of Debian that can run on your phone. The Maru app will run in the background and detect when an external display is connected. This tells it to spin up the debian OS. Then it must do something to connect to debian's desktop (vnc, nomachine, or proprietary solution), and output that solely to the secondary screen.
This last bit seems the most magical to me (and probably device dependent), but then again, my experience with android and secondary displays is somewhat limited to the mirroring that happens when you attach a monitor. Alternatively is the chromecast concept where your app turns into a control and the content is sent to the chromecast. Maybe the concept of running an app entirely on a second display is a native android concept these days.
Looks like there's a Presentation class [1] for activities meant to run on a second display. Also see [2], a presentation about it that mentions HDMI displays explicitly.
Here's one app called "Complete Linux Installer" (looks outdated) that does this: https://goo.gl/5ryu5x
It certainly works, though there has definitely been limitations caused by the speed of the hardware and the latency that vnc introduces. I've never tried this on an external monitor and external input devices. There's also a gap because you need a separate vnc client.
Maru, if it exists, seems to work off the same concept, but with some polish. They have an install of Debian that can run on your phone. The Maru app will run in the background and detect when an external display is connected. This tells it to spin up the debian OS. Then it must do something to connect to debian's desktop (vnc, nomachine, or proprietary solution), and output that solely to the secondary screen.
This last bit seems the most magical to me (and probably device dependent), but then again, my experience with android and secondary displays is somewhat limited to the mirroring that happens when you attach a monitor. Alternatively is the chromecast concept where your app turns into a control and the content is sent to the chromecast. Maybe the concept of running an app entirely on a second display is a native android concept these days.