Spacedesk

PC, android, and ipad/phone no mac support is the only drawback... but words so well. still deserves a 5 star rating. most useful free app. as of 2025 Rated top 10 apps by AaronGTV

This requires access to the Microsoft store on the secondary PC. In my case, my secondary PC is a company system on which the Microsoft store is completely blocked.

I also thoroughly hate their website. They spent so much effort on flashy animations, it makes it impossible to find information. They also don't publish any license pricing info, instead forcing you to use in-app purchases which is extremely sketchy IMO.

Every now and then, if you're anything like me, you to this website to see what you can find to make your life easier or to find something cool to show off to your friends and family to assert yourself further as the undisputed computer genius (lol not difficult when everyone else is 60+, but if I'm going to be the family tech support, things like this reminds them why they need to pay me for my assistance and hours upon hours of pure silly questions and issues haha).

Sorry about that tangent, anyway...

Spacedesk. Does exactly what it claims it does. Setup was done in roughly 3 minutes after I tinkered with the settings and it runs smooth and perfectly. Touchscreen functions retained. Since it's detected within Windows you can configure its placement in the monitor configuration screen, easy peasy.

As a test run I currently have my phone (S22 Ultra) functioning as a 3rd monitor below my second monitor and I have it so that my mouse has to go through the bottom of my second monitor to get to it:

[2nd][1st] [3rd]

It's pretty fun and awesome :) I strongly recommend if you need (or just plain want) something like this. Apparently it's unlimited too with how many screens you can connect (all wirelessly too, I might add) and you can mix/match vertical and horizontal orientations and resolutions as well.

Perfect ! Finally one software witch works to see the desktop of my PC even on a TV BOX of 512 MB the RAM !!!

I compared Spacedesk with Windows built-in Miracast. Overall, it works better unless you use a 4K screen.

Pro

• Flexible control of image quality: I can manually adjust image quality to fit in the bandwidth or keep the best quality. I can use the highest setting with a 900p screen on my 1Gb Ethernet. (It will sometimes freeze like what I write in the con below, though.) Miracast doesn't provide any settings.
• Responsive input: Input from viewer PC almost can't feel any lag in Ethernet mode. It will be a little laggy if you move the mouse from the viewer's PC when the mouse pointer is on the viewer screen because of image transfer delay. While Miracast's input from the viewer PC is very laggy and when the difference in the screen resolution is large, mouse movement will be jumpy.
• WIFI isn't a must: Miracast need WIFI to initiate the connection even in Ethernet mode.

Con

• Not optimized enough for screens with large resolution( or networks with low bandwidth): When I connected to my laptop with a 4K screen, everything was a lot worse than Miracast. I even bought a 1Gb network switch hoping it works better than Miracast but didn't. With a reasonable image quality, it couldn't achieve a smooth experience and would periodically freeze like 0.5 seconds. On the contrary, image responsiveness in Miracast is instant when gaming mode is selected (which IMH should always be selected) no matter what resolution is used. There is literally no lag. However, the overall smoothness or frame rate is lower. And Miracast performs surprisingly well in 4K. I feel the image quality is near 90/100 if in Spacedesk, with only a constant 3MB/s network traffic. While Spacedesk can take a range from 10MB/s to 40MB/s but performs worse.
• Doesn't support multi-touch: Neither does Miracast, though.

Its a great way to re purpose an old ipad/tablet and this app is the only one thats free and works relibly.

really wish linux was supported though