Often changing on a daily basis:
 

 
On top of the desks, from left to right:

• A Windows PC for gaming, heavy-duty web browsing, and TV (via a TV tuner card).
• A couple of 25" 1440p monitors. They're side-by-side, but I'm not actually using them for multi-monitor stuff! Left monitor is for Windows & 2 random ARM boards, right monitor is for Titanium, Iyonix, and 1 random ARM board.
• An old 15" DVI+VGA monitor (RiscPC + 1 random ARM board)
• An iMac and a couple of tablets for working from home during the pandemic
• A StrongARM RiscPC, generally only used for compatibility testing

If you look hard enough you should also be able to spot a BB-xM, IGEPv5, iMX6, Pandaboard, several Raspberry Pi's, and a USB switch which is used to allow the Iyonix & Titanium to share a keyboard.
 
Under the desk are the Iyonix, Titanium, and an ARMbook. The Titanium is my main RISC OS machine, although there's still lots of old stuff on the Iyonix that I haven't copied over yet. There's also a wireless keyboard/trackball combo that I use with the ARM boards - very useful for saving on desk space.
 
Out of frame there's another tower case which houses a headless Linux PC, which mainly gets used for source control stuff, GCC cross-compilation stuff, and as a general NAS.
 
Other Computer setups
 
If you want to add yours, send us send a pic and an intro on your RISC OS related setup (email to markstephens At idrsolutions.com), and we will add it.