With Barrier, I'm currently using 5 monitors between 3 computers as my main workstation--recently at one point I was using 10 monitors between about 5 to 7 computers. (Now my other computers are spaced out more around the house due to the type of projects I am currently working on--I might get more than 10 monitors and 7 computers going with Barrier simultaneously in the near future at some point though if I work on a project that could benefit from doing that.)
How Barrier Works:
"Barrier" is a fork of Synergy that is free software available on GitHub. It lets your mouse travel between monitors that are connected to 2 or more computers (and your keyboard follows the mouse and controls the computer of the monitor that the mouse is on at any given moment). With Barrier your mouse travels to the next computer's screen as if it is an external monitor that is actually attached to your main computer but you are really controlling the main computer and the external computers that are running on the same Barrier session with a single keyboard and mouse.
How I Use Barrier:
With Barrier, I run more intense stuff on the monitors that are plugged into the computers that are more powerful. Just plug in any computer and you have another full motherboard of computer power as well as more monitor workspace depending on how many monitors you might be able to plug into each computer you add to your Barrier session. Barrier has worked flawlessly for me with very few hitches over the last couple or years or so (my only main complaint is that I've have needed to reset my Barrier server software once every few days since it has a random freezing error but that's the main problem I've ever faced with it--it's tremendously reliable).
Using an old computer for another screen is great--have extra workspace for taking notes or doing light web browsing is very helpful at times--even to have glanceable reference without needing to tab between showing 2 different windows windows is tremendously convenient. All the more pixels to work with the better. I like having a lot of things open at once so I can reference things with my eyes at a moment's notice just by glancing at them. Text on your clipboard syncs with Barrier--so you can easily copy and paste text between computers at a moment's notice.
Really all that each of the systems do that run Barrier is track what computer the keyboard and mouse is on and make sure the clipboard between machines is in sync--very light on the resources of the computers running together on a Barrier session. No glitches, freezes, hot CPUs or loud fans from Barrier--and no choppy mouse and keyboard delays or video streaming needed like other windowed screen-sharing software that you'd otherwise get with things like VNC, RDP, LogMeIn, AirPlay, TeamViewer, Etc. No hassles of having multiple keyboards and mice on your desk to switch between computers or switching your keyboard and mouse to another computer that you'd otherwise get with things like a KVM switch. No need to deal with emulation slowdowns or hacks--you can run full systems just like they are regular external monitors on your main machine. Sure I use VMs, AirPlay, video switching hubs, TeamViewer, VNC and similar tools from time to time anyway but Barrier is a much better than a lot of these alternatives much of the time for the kinds of things I've done recently.
Barrier Works With All Mainstream Desktop and Mobile OSes:
I regularly used Barrier to connect Windows, Mac and Linux computers together to use simultaneously with a single keyboard and mouse on my desk. Barrier even connects to Android with software called "DeskDock" (which I have successfully used)--plus with Universal Control you can also control iPadOS with a single mouse and keyboard along with computers connected with Barrier. This means you can use a single keyboard and mouse to control Android, iPadOS, MacOS, Linux and Windows with one keyboard and mouse on a single connected bank of monitors with clipboard text support to seamlessly work across devices on screens with full frame-rates and with very minimal CPU use between systems.
